In the 1964 election, he was elected to the 89th United States Congress from New York and was re-elected twice. Ottinger gave up his House seat to run as the Democratic candidate for U.S. Senator from New York in 1970. Ottinger split the liberal vote with the Republican/Liberal candidate Charles Goodell (who had been appointed by Nelson Rockefeller to the seat), and both were defeated by the Conservative candidate, James L. Buckley.
Ottinger returned to the House of Representatives from a different New York district in the 1974 election, and was re-elected to the next four Congresses, retiring in 1985.
After retiring from Congress, Ottinger became a professor at Pace University School of Law, founding an environmental law program there, and served as the law school dean from 1994 to 1999. He currently serves as Dean Emeritus.