John O'Leary (1947 - 2 April 2005) served as mayor of Portland, Maine, and as United States ambassador to Chile under President Bill Clinton.
O'Leary was born in Portland and graduated from Yale University in 1969. He later attended Clare College, Cambridge University, on a Mellon fellowship and received a Master's degree in 1971. He received a degree from Yale Law School in 1974. While studying at Yale Law, O'Leary acted as a coach for the Yale Debate Team. He then went on to a private law practice.
He was an unsuccessful candidate for the U.S. House from Maine's First Congressional District in 1982, losing to Republican John R. McKernan, Jr..