Robert J. Birnbaum, who as president of the New York Stock Exchange is credited with helping to navigate a major financial crisis during the U.S. stock market’s plunge on what became known as Black Monday in 1987, and who later helped design market circuit breakers to head off future panics, died on Dec. 23 at his home in Boca Raton, FL. He was 94.

Mr. Birnbaum spent his career on Wall Street as one of its most reliable stewards. After studying the mechanics of marketplaces in the mid-20th century as a member of a special team at the Securities and Exchange Commission, he helped reshape stock exchanges while presiding over the American and New York exchanges.

When U.S. stock prices fell more than 22 percent on Oct. 19, 1987, his clear public comments helped soothe investors and prevent a frenzied sell-off from continuing. In the days that followed, Mr. Birnbaum played a crucial role in bringing together the leaders of various exchanges to hash out what had happened and how such a crisis could be averted in the future.