Michel Laclotte, who as director of the Louvre oversaw much of its historic renovations, and who earlier, as its chief curator of paintings, championed the Musée D’Orsay (the museum-in-a-train-station) and I.M. Pei’s glass pyramid at the Louvre — two of the most controversial but ultimately beloved architectural projects of late-20th-century Paris — died on Aug. 10 in Montauban, in southern France. He was 91.

Pierre Rosenberg, Mr. Laclotte’s successor at the Louvre, confirmed the death, at a friend’s home. No cause was given.

Mr. Laclotte went to battle for the Musée D’Orsay in 1972, after the French government had demolished the centuries-old market buildings at Les Halles. That had ignited a zeal for preservation in Paris rivaling that in New York City almost a decade earlier, when the old Penn Station, a Beaux-Arts landmark, was destroyed.

The Gare d’Orsay, a decommissioned train station on the left bank of the Seine, was facing the same fate when Mr. Laclotte had an epiphany: to turn that enormous and exuberant Beaux-Arts building into a museum.

He and his colleagues had already decided to expand the mission of the Jeu de Paume, a nearby offshoot of the Louvre that held the country’s collection of Impressionist paintings, to include other 19th-century work. For that Mr. Laclotte needed more space, and lots of it. The station seemed to fit the bill.

But there was also a thought in the air to turn the Gare d’Orsay into a hotel, or perhaps a center to promote products from the French provinces. Mr. Laclotte had to make a move.

As he recalled in “A Key to the Louvre: Memoirs of a Curator” (2004), he paid a visit to the minister in charge of greenlighting the project and made his plea: “Minister, you have to choose between Cézanne and reblochon cheese.”

Cheese lost.

It would be more than a decade before the Musée d’Orsay opened, in 1986, its interior having been reimagined by the Italian architect Gae Aulenti into a gutsy industrial space — essentially two rough stone galleries, which some critics likened to a funeral hall. The reviews were mixed.

Paul Goldberger of The New York Times described the galleries as bunkers, a “vaguely Egyptian version of postmodern architecture.” Some art critics carped over the collection, irritated by Mr. Laclotte and his colleagues’ decision to include a range of work from the mid-19th century to about 1915, rather than just the blue-chip Impressionists.

In any case, the public poured in, and Mr. Laclotte was proud of the passions his new museum seemed to inspire.

A few years after the Musée D’Orsay opened, he found himself with a group of American curator friends, two of whom were arguing about the museum. “One was shouting, ‘I hate Orsay,’ the other, ‘I love Orsay,’” he wrote in his memoir. “At that point, I said to myself that the battle was won. The museum inspired pleasure, interest and intellectual debate — exactly as we had wished.”

The debate around the Musée d’Orsay, however, was a tepid academic tiff compared with the one that erupted when plans for a multiphase renovation and expansion of the Louvre, called the Grand Louvre, were unveiled in the early 1980s. The vast, rambling palace that was the Louvre — the most famous art museum in the world and the home of the Mona Lisa — was by the 1970s cramped, dingy, disorganized and impossible to navigate. Mr. Laclotte described it as a sea serpent that he and his colleagues were forever wrangling.

One wing of the museum had been taken over by the Ministry of Finance, which turned it into a warren of offices. The Cour Napoleon, the Louvre’s central courtyard, was a parking lot by day and a gay cruising spot by night. When François Mitterrand, head of the country’s Socialist Party, was elected president in 1981, he gave his go-ahead for the renovation. (Large cultural institutions in France are run by the state.)

Émile Biasini, the administrator appointed to oversee the project, chose I.M. Pei to be its architect, embracing his plan for a starkly stunning modernist glass pyramid, to be built in the central courtyard as an elegant solution to the maze of the Louvre. Mr. Laclotte, who had admired Mr. Pei’s expansion of the National Gallery of Art in Washington, was thrilled by the design. Much of the rest of the country was not.

“A gigantic, ruinous gadget,” one critic lamented; another labeled it “Pharaoh Francois’s Pyramid.”

Worse, to many Parisians it was a foreign object designed by a foreigner: There could be no greater desecration to this exquisite French monument that was the cultural heart of Paris.

But Mr. Laclotte, ever diplomatic, took the storm in stride, even when a taxi driver, on learning who Mr. Laclotte was, berated him, shouting, “What you’re doing is criminal!”

“When you think about it, it wasn’t entirely unhealthy,” he wrote with his typical mildness. “It shows that the French public is interested in such cultural matters, even if it is ill informed or ill intentioned.”

Mr. Pei’s pyramid opened in 1989, and the fully renovated museum was reopened in 1993 (though work was to continue for several more years). Mr. Laclotte retired the next year. Mr. Rosenberg, his successor, said of him: “He created the modern Louvre. The image of Paris would not be what it is today without him.”

Michel Laclotte was born on Oct. 27, 1929, in Saint-Malo, a walled port city in Brittany. His father, Pierre, a lawyer, was killed in 1940 while fighting in World War II. The next year, Michel’s mother, Huguette (de Kermabon) Laclotte, moved Michel and his sister to Nazi-occupied Paris.

Michel first wanted to be an architect. But math was not his strong suit, so he decided instead on a career in museums, for which he studied at the École du Louvre. As a teenager, he would visit local museums on family vacations and reorganize them in his head. He kept copious notebooks on their collections.

“No doubt an adolescent passion for classification,” he said of his youthful habit. “And alongside this went a profound interest in the national patrimony.”

He began working at the Louvre in 1951 as an intern while still in school, giving guided tours and helping to document works in the painting department. One of his projects was to help identify works found in Germany that had been stolen from Jewish collectors.

The next year the government began a program to inspect museums that had been battered or destroyed in the war. Mr. Laclotte was chosen to direct the team that cataloged the artworks, or what was left of them, as well as to expand the collections and oversee the buildings’ restorations.

Still in his mid-30s, he was named director of paintings at the Louvre in 1966, one of the most important curatorial jobs in Europe. He became director of the museum in 1987.

Gary Tinterow, director of the Museum of Fine Arts in Houston, said in a phone interview that Mr. Laclotte “belongs to a truly remarkable generation of French museum curators and administrators who transformed French museology in the last quarter of the 20th century and created lasting institutions that led the Western world in innovation.”

Mr. Laclotte’s field of scholarship was Italian primitives. When he retired in 1994, he helped organize a national institute for art history, another complicated diplomatic mission. He avoided returning to the Louvre, he said, to spare himself the embarrassment of hearing former colleagues tell him, “Now you can do what you want!”

No immediate family members survive.

“He was a soft-spoken scholar,” Philippe de Montebello, the former director of the Metropolitan Museum of Art in New York, said by phone, “and if you were only to have a meal with him, it would have been very easy to think that he was just that: a bespectacled scholar in an ivory tower. The truth is, he turned out to have been an extraordinary man of action.”

In the spring of 1988, when the pyramid at the Louvre was nearly finished, Mr. Mitterrand arrived for a private viewing. As Mr. Laclotte recalled in his memoir, the president took the director aside and said, “Orsay and the Louvre — not bad for one career.”