He joined Lehman Brothers after serving as assistant to the President for International Economic Affairs, U.S. Secretary of Commerce, and President Nixon's ambassador and personal representative. Four years later, Peterson became chairman and CEO of Lehman Brothers, Kuhn, Loeb Inc. — a post he held from 1977 to 1983. During his tenure, he led the firm from significant operating losses to five consecutive years of record profits with the return on equity among the highest in the industry. He also served as chairman of the Blackstone Group, a private investment firm, and of Blackstone Capital Partners, a large fund engaged in principal activities.
Peterson was a director of several companies and a founding member of the Bipartisan Budget Appeal, an organization composed of five former secretaries of the Treasury and approximately five hundred leading Americans.
His many civic activities, from chairman of the Institute for International Economics to trustee of the Museum of Modern Art, reflect the broad range of his interests.