Downey graduated from West Islip High School, West Islip, New York, 1966; B.S., Cornell University, 1970; St. John's University Law School, Brooklyn, N.Y., 1972-1974; J.D., American University, 1980; served as Suffolk County, New York legislator, 1972-1974; delegate to Democratic National Convention, 1972; elected as a Democrat to the Ninety-fourth and to the eight succeeding Congresses (January 3, 1975-January 3, 1993); unsuccessful candidate for reelection to the One Hundred Third United States Congress in 1992; is a resident of West Islip, N.Y.

Downey made headlines in March 1985 for a confrontation with Representative Bob Dornan (R-CA) on the House floor. Downey asked Dornan about comments he had made calling Downey "a draft-dodging wimp". According to Downey, Dornan grabbed him by the collar and tie, said "It's good you're being protected by the sergeant-at-arms. If I saw you outside, it would be a different story," and threatened him "with some form of bodily harm". Dornan claimed he was merely straightening Downey's tie and refused to apologize for the incident or the derogatory comment. A Dornan aide said "It will be a cold day in hell before he gets an apology from Bob Dornan."

Downey is currently a lobbyist and chair of Downey McGrath Group, Inc., a lobbying firm he founded in 1993. The president is Ray McGrath, also a former US Representative from New York. Downey represented Dubai Ports World and lobbied Congress to approve the controversial ports deal. Downey argues that "they would have made this country more secure" because "DP World is one of the few companies that could have worked with us to truly improve security, both at home and abroad."