Born into a wealthy Paris family, Stern left the elite Paris postgraduate school Essec after a year to join the family bank. With the support of two uncles, he deposed his father as head of the business and sold it to Lebanese investors. He then joined Lazard, where he stayed for five years, marrying the chairman's daughter, Béatrice, a Sotheby's expert in European paintings, in 1983. He headed the group's US operation in New York.