Humphrey was born October 9, 1940, in Bristol, Connecticut. His first career path was in aviation: he served in the United States Air Force for several years and, following college, worked as a professional pilot. Despite being only a local Republican activist holding no political office, in 1978 Humphrey won election to the Senate by narrowly defeating three-term incumbent Thomas J. McIntyre by barely two percent. Humphrey was easily reelected in 1984, defeating five-term Democratic congressman Norman D'Amours.

In the Senate Humphrey served on both the Committee on Foreign Relations and the Armed Services Committee, and was a leader in the Congressional Task Force on Afghanistan, which shaped U.S. policy regarding the Soviet invasion of Afghanistan. He voted against the federal budget all 12 years he was a member of the Senate, each time because the proposed budget ran a deficit.

Humphrey declined to run for a third term in 1990, having promised only to serve two. He instead ran for and won a seat in the New Hampshire State Senate, the only former U.S. Senator to sit in a state senate. He served one term.

Humphrey returned to New Hampshire politics in 2000 by challenging incumbent Governor Jeanne Shaheen. Shaheen, a Democrat, was considered vulnerable in the wake of a State Supreme Court decision requiring the state to play a larger role in funding education, which many saw as a path toward instituting a statewide income or sales tax. Humphrey pledged to block attempts to enact such taxes, but was narrowly defeated in a contentious campaign.

He ran for the Republican nomination for governor again in 2002, but was outspent by businessman Craig Benson, who eventually won the nomination and the governor's race. Humphrey finished third, and said that the campaign would be his last.

He lives in New Hampshire with his wife, Patricia, and their two children.