Manatt was chairman of the Democratic National Committee from 1981 to 1985. In those years, he supervised and directed the 1984 Democratic National Convention. He was a delegate, sometimes categorized as a super delegate. He was the founder of the law firm Manatt, Phelps, and Phillips LLP, where his practice focused on international, administrative, and corporate law. He also served as ambassador to the Dominican Republic from 1999 to 2001. Manatt served until June 2008 as chairman of the board of trustees at the George Washington University. His widow is Kathleen K. Manatt.