Last summer, the chef Daniel Humm made a promise to himself. If he was going to reopen Eleven Madison Park, the Manhattan restaurant that has been called the best in the world, he was not going to return to importing caviar and braising celery root in pigs’ bladders.

On Monday, Mr. Humm announced that Eleven Madison Park, closed since last March by the pandemic, would reopen with a plant-based menu. It marks a striking departure for one of the most lavishly praised American restaurants of the past 20 years. An institution long known for the technical proficiency of dishes featuring suckling pig, sea urchin and lavender glazed duck will reopen with a menu free of meat and seafood.

Over the last 18 months, scrutiny of meat- and seafood-based diets for environmental and social reasons has intensified as the pandemic has exposed weaknesses in global food systems and underscored inequities in American life. Though Mr. Humm still offers plenty of red meat at his London restaurant, Davies and Brook at Claridge’s hotel, the move at Eleven Madison Park — which has four stars from The New York Times and three from Michelin — suggests how different fine dining may look as restaurants reopen and reimagine themselves.

Eleven Madison Park’s multicourse menu will keep its prepandemic price of $335, including tip. While a relatively minuscule number of diners will be able to afford such an expense at a restaurant where reservations have always been difficult to obtain, Mr. Humm is among a small number of chefs whose cultural influence extends beyond fine dining, said Paul Freedman, a professor of history at Yale University and the author of “Ten Restaurants That Changed America.”

He said that the new Eleven Madison Park will “have an influence on the best restaurants in places like Midland, Texas — affluent places that are not Los Angeles or San Francisco or New York.”

Ruth Reichl, the former editor of Gourmet magazine and restaurant critic for The New York Times from 1993 to 1999, said Mr. Humm’s example could influence the direction of American restaurant cuisine in the years ahead.

“A restaurant like Eleven Madison Park is basically a teaching institution,” Ms. Reichl said, likening its potential impact to that of Chez Panisse, the pioneering restaurant in Berkeley, Calif.

Mr. Humm said the decision is the result of a yearslong re-evaluation about where his career was headed, which reached its breaking point during the pandemic.

“It became very clear to me that our idea of what luxury is had to change,” Mr. Humm said. “We couldn’t go back to doing what we did before.”

While the restaurant’s ingredient costs will go down, labor costs will go up as Mr. Humm and his chefs work to make vegan food live up to Eleven Madison Park’s reputation. “It’s a labor intensive and time consuming process,” he said.

The restaurant will also help sustain Eleven Madison Truck, a mobile commissary kitchen Mr. Humm launched last spring, in partnership with Rethink Food, to address rising hunger needs in New York during the pandemic. Every meal purchased at Eleven Madison Park will provide five meals for that effort.

“I wanted everyone who comes into contact with Eleven Madison Park to become a part of doing good,” Mr. Humm said.

Jay Rayner, the restaurant critic for The Observer, in London, applauded Mr. Humm’s decision, but cautioned “there are limits to what you can do through the medium of a Michelin-starred restaurant.”

“Chefs should obviously continue sourcing their ingredients responsibly, in light of the climate emergency,” he continued. “But at the end of the day, you’re still cooking for rich people, and you might question their commitment to these things.”

Mr. Humm, who was born in Switzerland and cooks in a style developed in Western Europe, is far from the first chef of his stature to shift his focus to vegetables. Alain Passard has been serving a vegetable tasting menu at L’Arpège, his celebrated restaurant in Paris, since 2001. Ms. Reichl pointed out that Charlie Trotter was cooking similarly in the 1990s, in Chicago.

Amanda Cohen, the chef and owner of Dirt Candy, a vegetarian restaurant in New York City, said Mr. Humm’s decision is significant because he had not been previously associated with plant-based cuisine. “It continues to move the conversation forward,” she said.

Mr. Humm became executive chef at Eleven Madison Park in 2006, eight years after it was first opened by the restaurateur Danny Meyer. Mr. Humm and his then business partner, Will Guidara, purchased the restaurant from Mr. Meyer in 2011. The partners strove to land atop the annual list of the World’s 50 Best Restaurants.

Mr. Humm said the pressure that came with finally achieving that goal, in 2017, contributed to the split with Mr. Guidara in 2019.

In recent years, Mr. Humm has been dating Laurene Powell Jobs, the prominent philanthropist, founder of the Emerson Collective and widow of Steve Jobs. Ms. Jobs is not financially involved in Eleven Madison Park, he said.

Mr. Humm’s change in direction also comes as more prominent restaurants have shifted to plant-based menus, sometimes to critical applause.

The Bay Area chef Dominique Crenn made all of her restaurants meat-free in 2019. In January, the Michelin Guide gave its first star to a fully vegan establishment in France, ONA, a restaurant near Bordeaux. In February, the chef Ann Kim opened her new Minneapolis restaurant, Sooki & Mimi, with a vegetable and masa-based tasting menu.

Cooking publications and websites have made similar bets about diners’ priorities. Last month, Epicurious, the popular cooking website, said it would not publish new beef recipes and had been phasing them out for over a year over concerns about climate change. Epicurious cited data from the Food and Agriculture Organization of the United Nations that said 14.5 percent of global greenhouse gas emissions come from livestock.

But Eleven Madison Park will not be entirely free of animal products — they will continue to offer milk and honey for coffee and tea service — and Mr. Humm steers clear of the word “vegan,” which he thinks can have negative connotations.

“Eleven Madison Park is about surprising people,” Mr. Humm said. “We don’t want to lecture people.”