Ernesto Sabato, 99, a celebrated Argentine writer and intellectual who was chosen to lead an official investigation of thousands of killings by the military during the Dirty War of the 1970s and 1980s, and whose long life included careers as a physicist, public servant and artist, died April 30 at his home near Buenos Aires.

He had complications from bronchitis, according to the Associated Press.

Dr. Sabato took his place among Latin America’s greatest writers, such as Gabriel Garcia Marquez, Mario Vargas Llosa and Jorge Luis Borges, and he followed a singular literary path that distinguished him from the writers of the Latin American “boom” of the 1960s and 1970s whose work was often experimental, frequently incorporating anti-authoritarian themes.

His work earned the Cervantes Prize, the highest award for literature in the Spanish language, and praise from authors as varied as Thomas Mann, Albert Camus and Salman Rushdie.

Dr. Sabato’s best-known novels, “The Tunnel” and “On Heroes and Tombs,” were crime stories that ranged into fantasy and the surreal, while examining the depths of love, melancholy and murder. His articles and essays touched on philosophy and world literature, and his social criticism sometimes chided Borges and other fellow writers for failing to speak out on current events.

As Dr. Sabato emerged as a prominent Argentine intellectual, his politics often took center stage. He had been a Communist youth leader in the 1930s and was forced underground for a time when a military government took over the country; he abandoned the party five years later, appalled by Stalinism. He became a strong opponent of all forms of authoritarianism. His book, “The Other Face of Peronism,” published in 1956, examined the phenomenon of Juan Peron, the nation’s populist president, as Dr. Sabato sought common ground among Peronist supporters and opponents.

Although he and other well-heeled Argentines applauded the fall of Peron in a 1955 coup, he noted, “many millions of the dispossessed and workers shed tears at a moment that was hard and sobering for them.”

After another military junta left power in 1983, the newly elected president, Raul Alfonsin, appointed Dr. Sabato to the National Commission on the Disappearance of Persons. Voting Dr. Sabato as their leader, the commissioners gathered documents and assembled often-wrenching testimony from survivors and family members about those tortured, disappeared and killed by the military from 1976 to 1983.

So central was his role that the commission’s concluding document, “Nunca Mas” (Never Again), has come to be known as the Sabato Report. The report, published in 1984, shocked Argentinians with details of almost 9,000 disappearances and 300 secret interrogation sites across the country. It was the first effort to systematically describe and document the stories of the dead and disappeared; subsequent updates list as many as 30,000 deaths.

The Dirty War, Dr. Sabato wrote, “the most terrible [tragedy] our nation has ever suffered, will undoubtedly serve to help us understand that it is only democracy which can save a people from horror on this scale. . . . Only with democracy will we be certain that NEVER AGAIN will events such as these, which have made Argentina so sadly infamous throughout the world, be repeated in our nation.”

The Sabato Report was praised as a first step toward the return to the rule of law, but Dr. Sabato received criticism from left and right. The Mothers of the Plaza de Mayo, an organized group of women who protested the disappearance of their children during the Argentine dictatorship, rejected Dr. Sabato’s opening statement that Argentina “was torn by terror from both the extreme right and the far left” in the 1970s. They and many other Argentinians contended that the leftist threat was insignificant compared with the military response. Among those who disappeared were students, teachers, workers and other government opponents, few of whom were involved in an organized movement.

After one military supporter said the report appeased human rights groups, Dr. Sabato complained that the commission’s task was monumental — and thankless.

“This is like taking water from the sea with a bucket,” he said. “All we get are threats and insults.”

Ernesto Sabato was born June 24, 1911, in Rojas, a small town in the pampas about 160 miles from Buenos Aires. He was the 10th of 11 children born to Italian immigrants who owned the local flour mill. He entered the National University of La Plata in 1929, studying science and mathematics, although he told interviewers he had always preferred writing and painting.

He completed a doctorate in physics in 1937 and won a research fellowship at the prestigious Curie Laboratory in Paris. When friends encouraged him to leave France as war closed in, he continued his research at MIT. By that time, he wanted to escape the sciences.

“It makes me laugh and I feel disgusted with myself,” he wrote. He added that “war was approaching, a war in which science — which according to those gentlemen had come to free mankind from all its physical and metaphysical ailments — was going to be the instrument of mechanized slaughter.”

He returned to Argentina and taught physics at La Plata and Buenos Aires for five more years, earning money while jump-starting his literary career. He was fired from his teaching jobs in 1945 after protesting the killing of a student by authorities in Buenos Aires. The dismissal served as his chance for a clean break.

In 1948, he published “The Tunnel,” a 135-page novella that is the rambling confession of an artist imprisoned for murder, describing his deadly obsession with a beautiful married woman. The book was first published in the United States under the title “The Outsider.” “The Tunnel” was translated in many languages and had several movie versions.

Dr. Sabato’s second novel, “On Heroes and Tombs,” appeared in 1961. It is a tour de force involving a young man, Martin; the beautiful Alejandra; her insane father, Fernando; and Martin’s confessor, Bruno, a friend of all three. Again, crime and murder are close at hand.

Critics recognized Dr. Sabato’s unique role in literature.

“Sabato stands apart from most of the writers of the ‘Boom’ and for good reason,” author and literary critic Robert Coover wrote in the New York Times. “Not only does he not participate in their communal voice, he is at war with it.”

Dr. Sabato served short stints at U.N. Educational, Scientific and Cultural Organization, as a magazine editor and at the Argentine foreign ministry, but resigned in each case within months, complaining about bureaucracy or protesting policies.

He met his wife, Matilde Kusminsky, when she was still in high school; they married in 1936 and were together until her death in 1998. The older of their two sons, Jorge, a former Argentine government minister, died in a car crash in 1995. Their surviving son, Mario, is a filmmaker whose work includes a 2008 documentary, “Ernesto Sabato, Mi Padre” (Ernesto Sabato, My Father).

The younger Sabato told an interviewer at the Spanish newspaper El Pais that his father was hard to know, even for his son. The effort was to penetrate “what was going on behind those black glasses, who the person was behind that character, that statue.”

Mr. Sabato’s compact memoir, “Antes del Fin” (Before the End), published in 1998, is a sober leave-taking and assessment of the world. It contrasts his faith with his pessimistic view of politics, poverty and the environment.

In his later years, Dr. Sabato’s eyes began to fail, and he virtually stopped writing. He shifted to painting. His artwork, often depicting surreal, fantastic themes, sometimes including portraits of his literary heroes, has been exhibited worldwide alongside his books.

“What is admirable,” Dr. Sabato said, “is that man keeps fighting and creating beauty in the midst of a barbaric, hostile world.”