Ivan Dominic Illich was born on 4 September 1926 in Vienna, Austria, to Gian Pietro Ilic (Ivan Peter Illich) and Ellen Rose "Maexie" née Regenstreif-Ortlieb. His father was a civil engineer and a diplomat from a landed Catholic family of Dalmatia, with property in the city of Split and wine and olive oil estates on the island of Brač. His mother came from a Jewish family that had converted to Christianity from Germany and Austria-Hungary (Czernowitz, Bukowina). Ellen Illich was baptized Lutheran but converted to Catholicism upon marriage. Her father, Friedrich "Fritz" Regenstreif, was an industrialist who made his money in the lumber trade in Bosnia, later settling in Vienna, where he built an art nouveau villa.

Ellen Illich traveled to Vienna to be attended by the best doctors during birth. Ivan's father was not living in Central Europe at the time. When Ivan was three months old, he was taken along with his nurse to Split, Dalmatia (by then part of the Kingdom of Yugoslavia), to be shown to his paternal grandfather. There he was baptized on 1 December 1926. In 1929 twin boys, Alexander and Michael, were born in the family.

In 1942, Ellen Illich and her three children—Ivan, Alexander, and Michael—left Vienna, Austria for Florence, Italy, escaping the Nazi persecution of Jews. Illich finished high school in Florence, and then went on to study histology and crystallography at the local University of Florence. Hoping to return to Austria following World War II, he enrolled in a doctorate in medieval history at the University of Salzburg with the hope of gaining legal residency as he was undocumented. He wrote a dissertation focusing on the historian Arnold J. Toynbee, a subject to which he would return in his later years. While working on his doctorate, he returned to Italy where he studied theology and philosophy at the Pontifical Gregorian University in Rome, as he wanted to become a Catholic priest. He was ordained as a Catholic priest in Rome in 1951 and served his first Mass in the catacombs where the early Roman Christians hid from their persecutors.

A polyglot, Illich spoke Italian, Spanish, French, and German fluently. He later learned Croatian, the language of his grandfathers, then Ancient Greek and Latin, in addition to Portuguese, Hindi, English, and other languages.

Following his ordination in 1951, he "signed up to become a parish priest in one of New York's poorest neighborhoods—Washington Heights, on the northern tip of Manhattan, at that time a barrio of newly-arrived Puerto Rican immigrants." In 1956, at the age of 30, he was appointed vice rector of the Catholic University of Puerto Rico, "a position he managed to keep for several years before getting thrown out—Illich was just a little too loud in his criticism of the Vatican's pronouncements on birth control and comparatively demure silence about the nuclear bomb." It was in Puerto Rico that Illich met Everett Reimer, and the two began to analyze their own functions as "educational" leaders. In 1959, he traveled throughout South America on foot and by bus.

The end of Illich's tenure at the university came in 1960 as the result of a controversy involving bishops James Edward McManus and James Peter Davis, who had denounced Governor Luis Muñoz Marín and his Popular Democratic Party for their positions in favor of birth control and divorce. The bishops also started their own rival Catholic party. Illich later summarized his opposition:

As a historian, I saw that it violated the American tradition of Church and State separation. As a politician, I predicted that there wasn't enough strength in Catholic ranks to create a meaningful platform and that failure of McManus's party would be disastrous on the already frail prestige of the Puerto Rican Church. As a theologian, I believe that the Church must always condemn injustice in the light of the Gospel, but never has the right to speak in favor of a specific political party.

After Illich disobeyed a direct order from McManus forbidding all priests from dining with Governor Muñoz, McManus ordered Illich to leave his post at the university, describing his presence as "dangerous to the Diocese of Ponce and its institutions."

Despite this display of insubordination and an order from Paul Francis Tanner, then general secretary of the National Catholic Welfare Conference, forbidding Illich from any official role in the organization's Latin American bureau, Illich maintained the support of the influential priest John J. Considine, who continued to push for Illich to have a role in training the Church's missionaries, personally funding trips to Mexico in order for Illich to scout locations.

Following his departure from Puerto Rico, Illich moved to Cuernavaca, Mexico, where he founded the Center of Intercultural Formation (CIF) in 1961, originally as a missionary training center. As the center became more influential, it became the Centro Intercultural de Documentación (CIDOC, or Intercultural Documentation Center), ostensibly a research center offering language courses to missionaries from North America and volunteers of the Alliance for Progress program initiated by John F. Kennedy. His real intent was to document the participation of the Vatican in the "modern development" of the so-called Third World. Illich looked askance at the liberal pity or conservative imperiousness that motivated the rising tide of global industrial development. He viewed such emissaries as a form of industrial hegemony and, as such, an act of "war on subsistence". He sought to teach missionaries dispatched by the Church not to impose their own cultural values. "Throughout the late 1960s and early 1970s, CIDOC was part language school and part free university for intellectuals from all over the Americas." At the CIDOC, "Illich was able to develop his potent and highly influential critique of Third World development schemes and their fresh-faced agents: Kennedy's Alliance for Progress, the Peace Corps, and countless other missionary efforts bankrolled and organized by wealthy nations, foundations, and religious groups."

After ten years, critical analysis from the CIDOC of the institutional actions by the Church brought the organization into conflict with the Vatican. Unpopular with the local chapter of Opus Dei, Illich was called to Rome for questioning, due in part to a CIA report. While he was not convicted or punished by the Vatican, it was then that he decided to renounce active priesthood. In 1976, apparently concerned by the influx of formal academics and the potential side effects of its own "institutionalization", Illich shut the center down with consent from the other members of the CIDOC. Several of the members subsequently continued language schools in Cuernavaca, some of which still exist. Illich, who had been made a monsignor at 33, himself resigned from the active priesthood in the late 1960s but continued to identify as a priest and occasionally performed private masses.

In the 1970s, Illich was popular among leftist intellectuals in France, his thesis having been discussed in particular by André Gorz. However, his influence declined after the 1981 election of François Mitterrand, as Illich was considered too pessimistic at a time when the French Left took control of the government.

In the 1980s and beyond, Illich traveled extensively, mainly splitting his time between the United States, Mexico, and Germany. He held an appointment as a Visiting Professor of Philosophy, Science, Technology, and Society at Penn State. He also taught at the University of Bremen and University of Hagen. During the last days of his life he admitted that he was greatly influenced by one of the Indian economists and adviser to M. K. Gandhi, J. C. Kumarappa, most notably his book, Economy of Permanence.

While Illich never referred to himself as an anarchist in print, he was closely associated with major figures in left-anarchist circles, notably Paul Goodman and unschooling advocate John Holt. Goodman is credited in Deschooling Society with having "radically obliged" Illich to revise his thinking and is described with great affection in Illich's 1990s interviews with David Cayley:

... I loved Goodman very much, but not from the beginning. In 1951, as a twenty-six-year-old man newly arrived in New York, I went to a public debate. This strange person arrived and fascinated everybody with his way of presenting himself. I was just then having my first experiences of sitting through cold turkey with neighbourhood kids from Washington Heights, and this guy carefully phrased his proposal that New York immediately decriminalize all substances you can ingest, because otherwise the city of New York would become an unlivable city within the next few years. He had recently played a major part in getting a law passed which recognized that the state should not interfere with the private activities of consenting adults. Well, I was shocked! I would not have suspected that within three of four years we would be good friends and that during the last part of his life he would spend considerable time with me in Cuernavaca. I consider Goodman one of the great thinkers I've known, and also a tender, touching person.

Ivan Illich called himself "an errant pilgrim", "a wandering Jew and a Christian pilgrim", while clearly acknowledging his Dalmatian roots. He remarked that since leaving the old house of his grandparents on the island Brač in Dalmatia, he had never had a home.

Illich died on 2 December 2002 in Bremen, Germany. Not realised was his last wish: to die surrounded by close collaborators in Bologna amid the creation of his planned, new learning centre.

Illich gained public attention with his 1971 book Deschooling Society, a radical critique of educational practice in "modern" economies. Claiming examples of institutionalised education's ineffectiveness, Illich endorses self-directed education, supported by intentional social relations, in fluid informal arrangements:

Universal education through schooling is not feasible. It would be no more feasible if it were attempted by means of alternative institutions built on the style of present schools. Neither new attitudes of teachers toward their pupils nor the proliferation of educational hardware or software (in classroom or bedroom), nor finally the attempt to expand the pedagogue's responsibility until it engulfs his pupils' lifetimes will deliver universal education. The current search for new educational funnels must be reversed into the search for their institutional inverse: educational webs which heighten the opportunity for each one to transform each moment of his living into one of learning, sharing, and caring. We hope to contribute concepts needed by those who conduct such counterfoil research on education—and also to those who seek alternatives to other established service industries.

The final sentence, above, clarifies Illich's view that education's institutionalisation fosters society's institutionalisation, and so de-institutionalising education may help de-institutionalize society. Further, Illich suggests reinventing learning and expanding it throughout society and across persons' lifespans. Particularly striking in 1971 was his call for advanced technology to support "learning webs":

The operation of a peer-matching network would be simple. The user would identify himself by name and address and describe the activity for which he sought a peer. A computer would send him back the names and addresses of all those who had inserted the same description. It is amazing that such a simple utility has never been used on a broad scale for publicly valued activity.

According to a contemporary review in the Libertarian Forum, "Illich's advocacy of the free market in education is the bone in the throat that is choking the public educators." Yet, unlike libertarians, Illich opposes not merely publicly funded schooling, but schools as such. Thus, Illich's envisioned disestablishment of schools aimed not to establish a free market in educational services, but to attain a fundamental shift: a deschooled society. In his 1973 book After Deschooling, What?, he asserted, "We can disestablish schools, or we can deschool culture." In fact, he called advocates of free-market education "the most dangerous category of educational reformers."

Tools for Conviviality was published in 1973, two years after Deschooling Society. In this newer work, Illich generalizes the themes that he had previously applied to the educational field: the institutionalization of specialized knowledge, the dominant role of technocratic elites in industrial society, and the need to develop new instruments for the reconquest of practical knowledge by the average citizen. He wrote that "[e]lite professional groups ... have come to exert a 'radical monopoly' on such basic human activities as health, agriculture, home-building, and learning, leading to a 'war on subsistence' that robs peasant societies of their vital skills and know-how. The result of much economic development is very often not human flourishing but 'modernized poverty', dependency, and an out-of-control system in which the humans become worn-down mechanical parts." Illich proposed that we should "invert the present deep structure of tools" in order to "give people tools that guarantee their right to work with independent efficiency."

Tools for Conviviality attracted worldwide attention. A résumé of it was published by French social philosopher André Gorz in Les Temps Modernes, under the title "Freeing the Future". The book's vision of tools that would be developed and maintained by a community of users had a significant influence on the first developers of the personal computer, notably Lee Felsenstein.

In his Medical Nemesis, first published in 1975, also known as Limits to Medicine, Illich subjected contemporary Western medicine to detailed attack. He argued that the medicalization in recent decades of so many of life's vicissitudes—birth and death, for example—frequently caused more harm than good and rendered many people in effect lifelong patients. He marshalled a body of statistics to show what he considered the shocking extent of post-operative side-effects and drug-induced illness in advanced industrial society. He introduced to a wider public the notion of iatrogenic disease, which had been scientifically established a century earlier by British nurse Florence Nightingale (1820–1910). Others have since voiced similar views.

In his 1968 speech at the Conference on InterAmerican Student Projects (CIASP), Illich strongly opposes the presence of American Roman Catholic missionaries, the Peace Corps and organizations like the CIASP themselves who invited him to speak- in Mexico. Illich says that the presence of American "do-gooders" is causing more harm than good. Rather, he suggests that the Americans should travel to Latin America as tourists or students, or else stay in their homeland, where they can at least know what they are doing.

Illich defined conviviality as “autonomous and creative intercourse among persons, and the intercourse of persons with their environment.” He contrasted this to “the conditioned response of persons to the demands made upon them by others” from above and afar in the name of advancing progress. “I consider conviviality to be individual freedom realized in personal interdependence and, as such, an intrinsic ethical value,” he wrote in “Tools for Conviviality.” “I believe that, in any society, as conviviality is reduced below a certain level, no amount of industrial productivity can effectively satisfy the needs it creates among society’s members.” 

Illich didn’t stop there. His greatest insight was that when conviviality is swapped for productivity, monopolizing institutions that chart a singular path at mass scale become counterproductive to their original intent beyond a certain threshold. In his words, “By breaching the limits set on man by nature and history, industrial society engendered disability and suffering in the name of eliminating disability and suffering. … The warming biosphere is making it intolerable to think of industrial growth as progress; now it appears to us as aggression against the human condition.” 

In his book “Energy and Equity” Illich illustrated this point in terms all could easily understand. As anyone who has driven on a freeway would agree, individual mobility turns into collective congestion when everyone has a car. In this he was in league with the “small is beautiful” thinkers at the time such as Leopold Kohr and E. F. Schumacher. 

In his radically provocative way, Illich preached the “virtue of enoughness” as the frugal way out of a headlong rush to an untenable future. Indeed, in the 1980s he subsisted in the small hamlet of Ocotepec, about 50 miles from Mexico City, where I visited him one summer along with my wife Lilly and former California Governor Jerry Brown. The streets were unpaved with no streetlights. Packs of feral dogs, chickens and the odd burro roamed freely. Scorpions scuttled across the floors and walls. The austere room where Illich slept was adorned with nothing other than a massive crucifix. At the back of the compound, incongruously, stood a rustic library filled with rare Latin volumes where he labored in “the vineyard of the texts” like one of his idols, Hugh of Saint Victor. Over lunches of watery lentil soup and weak fruit juice, he would often invite over the “Red Bishops” of Cuernavaca and Chiapas for convivial banter. At night we would sit up drinking cheap Presidente brandy, pondering the fate of civilization.

Illich carried his theme across the entire institutional landscape of modern society. In one of his most famously controversial books, “Deschooling Society,” he argued that the graduated credentialism of mass education actually made people more ignorant by standardizing what they can know and think about.

In those early days of cybernetics, he hoped that the recursive feedback loops of information systems might help foster an “ecology of mind,” as the anthropologist Gregory Bateson framed it, re-embedding the person in the larger matrix of being. Yet he suspected in the end it would not turn out so well, instead feeding the illusion that humans could escape the limits of their condition through their tools. As we have now come to see, the algorithms of Big Tech are, after all, only mathematical institutions programmed to bolster the very modern certitudes Illich fundamentally questioned, accelerating “progress” along an unsustainable trajectory that would continue to wreak ruin on the planet and reduce, not enhance, personal autonomy.

Here, too, he echoed other thinkers of his time like Jacques Ellul. The French theologian anticipated the surveillance capitalism of the digital age, believing that a technological society ends up imprisoning personal self-determination instead of liberating it.  

It was perhaps with respect to health that Illich was most radical. He decried “the sacralization of ‘a life’” dis-embedded from the oneness of Life and fetishized as a detached immune system to be managed from sperm to worm by the “brave new biocracy” of modern medicine. 

For Illich, vaccines, clean water and simple hygiene like washing hands were responsible for most health advances. But he was blistering in his critique of our medical systems oriented toward postponing the end as long as possible. “We now see that a majority of these medical achievements are deceptive misnomers, actually prolonging the suffering of madmen, cripples, old fools and monsters,” he wrote. 

In his book “Medical Nemesis” Illich spoke of “iatrogenic illness” — illness caused by the “bureaucracy” of physicians who abandoned the ancient idea of health as “balance” within the environment in which a person lived. Such a healthy balance could not be achieved, he argued, in an unhealthy environment poisoned by untamed industrial growth. 

Illich walked the talk. He suffered in his last years from a cancerous tumor that grew to the size of a baseball on one side of his face. “Renouncing” the biocratic management of his health, Illich insisted on the “hygienic autonomy” of self-care and “the right to die without diagnosis.” When the pain was too great during the final phase of his life, he would seek relief by standing on his head against a wall or by smoking opium in a little pipe he carried around with him.

In his more obscure and less public observations, Illich saw the Catholic Church’s depersonalized “kindness of strangers” as a corruption of the Christian act of charity institutionalized as a kind of inauthentic paternalism. In his book, Cayley suggests that Illich’s broad critique of the institutions of Western modernity were metaphors for an attack on the Catholic Church’s perversion of the personal experience of incarnation he was unwilling to make frontally, a kind of hidden theology that threaded through all his work. To the extent this errant pilgrim’s critique of the splintering and shattering of the oneness of Life can be considered theology, it is not so much hidden as constitutive of all Illich’s thinking. 

One does not have to embrace Illich’s romanticization of premodern times to grasp his relevance for the future headed our way. We appear to be entering a new pivotal age in which the modern certitudes he so thoroughly questioned are near exhaustion, finally opening the social imagination to the kind of fundamental reconsideration that seemed so radical in Illich’s day, but no longer do.