In a statement Wednesday, Lazard's board said the cause of death had not yet been determined. It didn't say where Wasserstein died.
Steven J. Golub, vice chairman of Lazard, was named interim chief executive, effective immediately, the statement said.
Golub, 63, has been with the company since 1984 and has served as chief financial officer and chairman of Lazard's Financial Advisory business.
A onetime corporate lawyer, Wasserstein rose to the top of the ranks of merger advisors during the 1980s and won a well-publicized battle with Michel David-Weill to take Lazard Freres & Co. public. He became chairman and chief executive in May 2005.
Wasserstein used his wealth from his investments to become a media owner, buying New York magazine for $55 million in 2003. He paid $63 million for American Lawyer and $200 million for National Law Publishing Co. in 1997 and sold those publications to Incisive Media of the United Kingdom for $630 million.
Most recently, Wasserstein was personally leading the team advising Kraft Foods Inc. Chief Executive Irene Rosenfeld on her $16-billion takeover bid for British chocolate maker Cadbury PLC.
A Wall Street superstar since the 1980s, Wasserstein worked on such landmark deals as Kohlberg Kravis Roberts' takeover of RJR Nabisco, and the Morgan Stanley-Dean Witter and AOL-Time Warner mergers.
"Bruce brought with him this combination of very, very complete technical knowledge of the law, and at the same time he was very imaginative in the kinds of deals and takeovers that he advised clients on," Felix Rohatyn, a former managing director of Lazard, told Bloomberg Television. "It's a big loss."
The New York native learned mergers and acquisitions at First Boston Corp., now part of Credit Suisse, and left with Joseph Perella in 1988 to found Wasserstein, Perella & Co.
Germany's Dresdner Bank bought Wasserstein, Perella for $1.56 billion in 2001, moving Wasserstein into the ranks of the wealthiest people in the United States.
Last month, Forbes magazine estimated his net worth to be $2.3 billion, tied for 190th on its annual list of the 400 richest Americans.
Bruce Jay Wasserstein was born Dec. 25, 1947, in the New York City borough of Brooklyn. His father, Morris, was an immigrant from Poland who had started a ribbon company with his brothers.
After the death of his oldest brother, Morris married his widowed sister-in-law, Lola, and became father to their two children, according to William Cohan's 2007 book "The Last Tycoons: The Secret History of Lazard Freres & Co."
Together, Morris and Lola had three more children -- Bruce, Georgette and Wendy, the playwright whose works included "The Heidi Chronicles," which won a Tony Award and a Pulitzer Prize. She died in 2006 from complications of lymphoma.
The family moved to Manhattan while Bruce Wasserstein was in high school.
He entered the University of Michigan at age 16, majoring in political science and ascending to executive editor of the student newspaper. He weighed becoming a journalist.
At Harvard University Law School, he entered a dual-degree program in law and business and graduated in 1971 with a law degree, cum laude, and a master's in business administration, with high distinction.
Through a summer job at Ralph Nader's consumer-advocacy organization Public Citizen, Wasserstein met Mark Green, later to become New York City's public advocate.
They co-edited "With Justice for Some: An Indictment of the Law by Young Advocates" and co-wrote "The Closed Enterprise System," which argued that lax antitrust enforcement led to monopolies and inflated prices.
In 2007, Wasserstein donated $25 million to Harvard Law School for construction of a new academic center. It was the second-largest gift in the history of the law school. He also was a major donor to the Democratic Party.
Wasserstein's first three marriages ended in divorce. He married Angela Chao earlier this year.
He is survived by his wife and seven children, including the daughter of his late sister Wendy whom he adopted, the New York Times reported.