Hinchey was born in New York City, but has spent most of his life in Saugerties. After serving in the United States Navy (1958-59), he spent two years working as a laborer in a cement plant. He graduated from the State University of New York at New Paltz with a B.A. in 1968 and an M.A. in 1970.

Hinchey worked with his father and others to strengthen the Democratic Party in Saugerties, a traditionally Republican town. He held positions in the Ulster County Democratic Party and managed a campaign for a friend. He first sought public office himself in 1972, with an unsuccessful race for the New York State Assembly. He ran again in 1974 and won, becoming the first Democrat elected to represent Ulster County in the state legislature since 1912. He served in the Assembly for eighteen years. He was particularly noted for his work on protecting the natural environment. For fourteen years he chaired the Committee on Environmental Conservation. One highlight of his tenure was the passage of the country's first law concerning regulation of acid rain. His committee also gained public attention for its investigation of the infiltration of the waste removal industry by organized crime.

In 1992, 28th District Congressman Matt McHugh retired after 18 years in the House. Hinchey won the Democratic nomination for the district, which had been renumbered the 26th after New York lost three districts as a result of the 1990 census. He handily defeated Republican Robert Moppert, a county legislator in Broome County (which includes Binghamton), in the November general election. He faced Moppert again in 1994, the midterm election in which the Republicans took control of the House. Hinchey won re-election by only 1,200 votes, but has not faced another serious contest.

The Congressional district was significantly reconfigured when New York lost two Congressional seats after the 2000 census. Hinchey was threatened with dismemberment of his district or with having to run against a popular and well-established Republican incumbent, either Ben Gilman or Sherwood Boehlert. In the intense political infighting over the redistricting, however, Hinchey emerged as one of the winners. To protect two younger Republican incumbents, the Republicans agreed to sacrifice the district of the 79-year-old Gilman, who chose to retire. In return, the Democrats accepted a district that threw together two of their incumbents, Louise Slaughter and John LaFalce, prompting the latter's retirement. Hinchey's district was renumbered the 22nd and winds a narrow, contorted path across eight counties in the southern part of the state, from the Hudson River to the Finger Lakes.

Hinchey has run in historically Republican areas throughout his career (his district was held by Republicans from 1915 until McHugh won it for the Democrats in 1975). However, he does not bill himself as a conservative or even a moderate Democrat. In fact, he is one of the most liberal members of the House, and one of the state's most liberal congressmen outside New York City. For example, his website states, "He was one of the first and most outspoken opponents of the 2003 war in Iraq." He has bridged the ideological gap partly by placing a heavy emphasis on constituent service. He now serves on the powerful Appropriations Committee, a post that helps him deliver federal support on programs important to his district.