Pierre Sylvain Désiré Gérard David-Weill was born on 8 March 1900 in Paris, France, into a Jewish family.
His father, David David-Weill (1871-1952), was the chairman of Lazard Frères; his mother was Flora Raphaël.
Along with Lazard Frères minority partner, André Meyer, Pierre David-Weill and his family fled the German occupation of France during World War II to the safety of the United States.
There, he took charge of the firm's office in New York City, where he remained until the liberation of France by Allied Forces in 1944.
On his return to Paris, he left André Meyer in charge of American operations, and along with Felix Rohatyn, they expanded the Lazard Frères business to make it a leading Euro-American investment bank.