After stints in the British and Canadian navies, he considered becoming a Catholic priest, ultimately deciding he was not meant for the seminary. He found a degree of meaning teaching philosophy in Toronto. But his life took a new direction in the early 1960s, when he traveled to France to see his spiritual mentor, a member of the Dominican order then serving as a chaplain at a home for people with intellectual disabilities.

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At the chaplain’s urging, Mr. Vanier, then in his mid-30s, began visiting French asylums. He found what he described as a “chaotic atmosphere of violence and uproar.” Some patients were shackled. Those who were not did little but walk in circles. Especially disturbing to Mr. Vanier was their screams.

The scene was typical of mental institutions around the world at the time. Underfunded and largely unregulated, they were used indiscriminately to house people with mental illness, intellectual disabilities, dementia and other conditions or proclivities that made them undesirable to society.

In witnessing their suffering, Mr. Vanier discovered a profound affinity for disabled people and saw them, he later wrote, as a “source of life and truth, if we welcome them . . . and put ourselves at their service.”

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He resolved to build a community where people with and without intellectual disabilities could live and work alongside one another as equals. With financial help from his parents and other patrons, Mr. Vanier bought what he called a “dilapidated” house in the French town of Trosly-Breuil, northeast of Paris, initially with no electricity or running water. The first two residents, one mentally and physically disabled by meningitis and the other by encephalitis, came from an overcrowded psychiatric hospital.

That house was the first of 154 communities across 38 countries that today form the network known as L’Arche International — French for the ark that saved Noah and the animals during the flood recounted in the Old Testament book of Genesis.

Mr. Vanier, who in 2015 received the Templeton Prize honoring “exceptional contribution to affirming life’s spiritual dimension,” died May 7 at a medical center in Paris at 90. The prize, bestowed by the U.S.-based John Templeton Foundation, was worth approximately $1.7 million.

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Michael W. Higgins, a biographer of Mr. Vanier’s, said in an interview that the Vanier family occupied in Canada a place similar to that of the Kennedys among American Catholics. “The name has an incredible luster to it,” he said, and yet Mr. Vanier “never invoked privileged status or position.”

He began his work just as deinstitutionalization, which called for patients to be removed from psychiatric hospitals and integrated into the community, began to take hold internationally. Margaret A. Nygren, the executive director of the American Association on Intellectual and Developmental Disabilities, placed him “at the forefront of a grass-roots movement” toward that end.

As Mr. Vanier shed the habits of a naval officer to live more collaboratively with other L’Arche residents, he arrived at the fundamental realization that would inform his mission.

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“The balance of our world frequently is seen as a question of power. That if I have more power and more knowledge, more capacity, then I can do more,” he once told Krista Tippett, host of the public radio program and podcast now called “On Being.” But “when you have power, we can very quickly push people down,” he continued. “And this is the history of humanity.”

Although driven by his Catholic faith, Mr. Vanier gradually led the L’Arche network into more ecumenical work. Observers described his theology as one of simple, concrete, tender acts: bathing a fellow human being, dining together, offering a reassuring touch.

Other humanitarians approached people with disabilities “either from the philanthropic or the altruistic point of view,” Higgins said, complacent in the assumption that it fell to the powerful to help the powerless. Mr. Vanier upended that philosophy “by saying that no, those who have the power — those who are able — need the disabled and the powerless” and that “they give us gifts we couldn’t have otherwise.”

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Mr. Vanier conceded L’Arche communities were not utopias. One of his earlier core members, as residents with disabilities were known, could not hear or speak and was so unsettled by his new environment that he escaped at night and had to return to a mental institution.

“As we share our lives with the powerless, we are obliged to leave behind our theories about the world, our dreams and our beautiful thoughts about God,” Mr. Vanier observed, “to become grounded in a reality that can be quite harsh.”

He found that his work was transformative not only for people with disabilities but also for their assistants. Assistants often would live in L’Arche communities for a year or two, although some have stayed for decades. According to the organization, L’Arche communities have 10,000 members worldwide, including core members and assistants.

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The intimate and personalized nature of L’Arche communities does not lend itself to the comprehensive tracking of outcomes and benefits, according to Nygren. But she said the organization is well-regarded — a “very forward-thinking, very innovative” attempt at building community life for people with intellectual and developmental disabilities.

“When those ingrained in a culture of winning and of individual success really meet them, and enter into friendship with them, something amazing and wonderful happens,” Mr. Vanier said at a news conference when he received the Templeton Prize. “They too are opened up to love and even to God. They are changed at a very deep level. They are transformed and become more fundamentally human.”

Jean François Antoine Vanier was born on Sept. 10, 1928, in Geneva, where his father, Georges Vanier, was posted with the League of Nations. His mother, the former Pauline Archer, came from a prominent Quebecois family. The couple had five children, including a daughter who became a hematologist and three other sons who became, respectively, a Trappist monk, an abstract painter and a political scientist.

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Mr. Vanier spent part of his childhood in England and then in France until the perils of World War II sent the family back to Canada. At 13, Mr. Vanier declared that he wished to return to England and enroll at Britain’s Royal Naval College at Dartmouth. The trip would entail braving the U-boats that menaced the Atlantic waters. But Mr. Vanier’s father, who had lost a leg during military service in World War I, agreed.

“I trust you,” Mr. Vanier recalled his father saying, according to the Toronto Star — an act he said gave him confidence to last him through each stop in his peripatetic early life.

The war had ended by the time Mr. Vanier completed his military training. He was a junior officer aboard an aircraft carrier before leaving the military after a 30-day Ignatian retreat. He told Tippett that navy service had made him “a man who knew how to be efficient and quick,” one who “knew how to give commands,” but one who lacked meaningful relationships in his life before he founded L’Arche. He never married and had no immediate survivors.

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After resigning his commission in 1950, Mr. Vanier studied at Eau Vive, a contemplative community near Paris, and later lived at a Trappist monastery. He enrolled at the Institut Catholique in Paris, receiving a doctorate in 1962 with a dissertation on Aristotle, and taught Aristotelian ethics at the University of St. Michael’s College at the University of Toronto before returning to France to found L’Arche.

“I knew it was an irreversible act,” he told the Herald of Glasgow, Scotland, in 1998. “But I did not know that L’Arche would grow as it has.”

Mr. Vanier’s death was announced by Theo Latiolais, a spokesman for L’Arche USA, who said Mr. Vanier had thyroid cancer.

He had lived until several years ago at the L’Arche home in Trosly-Breuil. The residents there and the disabled everywhere, he said, are “seeking friendship. It’s a message for all of us. It’s about all of us.”

CORRECTION: An earlier version of this obituary incorrectly reported that Mr. Vanier commanded an aircraft carrier. He was a junior officer aboard an aircraft carrier before leaving the military.