In one of the most significant gifts in the history of the Metropolitan Museum of Art, the philanthropist and cosmetics tycoon Leonard A. Lauder has promised the institution his collection of 78 Cubist paintings, drawings and sculptures.

The trove of signature works, which includes 33 Picassos, 17 Braques, 14 Légers and 14 works by Gris, is valued at more than $1 billion. It puts Mr. Lauder, who for years has been one of the city’s most influential art patrons, in a class with cornerstone contributors to the museum like Michael C. Rockefeller, Walter Annenberg, Henry Osborne Havemeyer and Robert Lehman.

The gift was approved by the Met’s board at a meeting Tuesday afternoon.

Scholars say the collection is among the world’s greatest, as good as, if not better than, the renowned Cubist paintings, drawings and sculptures in institutions like the Museum of Modern Art in New York, the State Hermitage Museum in St. Petersburg and the Pompidou Center in Paris. Together they tell the story of a movement that revolutionized Modern art and fill a glaring gap in the Met’s collection, which has been notably weak in early-20th-century art.

“In one fell swoop this puts the Met at the forefront of early-20th-century art,” Thomas P. Campbell, the Met’s director, said. “It is an unreproducible collection, something museum directors only dream about.”