Gallen had a successful tryout with the Washington Senators baseball team—signed to a minor-league contract as a pitcher in February 1947,[1] he played for their Kingsport Cherokees affiliate for part of that season,[2] but an arm injury ended his career.

Gallen worked as a truck driver, carpenter, and laborer in a paper mill before entering the auto sales industry, buying a General Motors dealership in Littleton.

Gallen ran for a third term in 1982, facing former state representative and Tufts University professor John H. Sununu in the general election.

In his first term, Gallen pushed through legislation preventing the Public Service Company of New Hampshire from increasing rates to fund construction of the Seabrook Station Nuclear Power Plant.

in March 1980 Gallen and other officials were made targets for harassing telephone calls according to a list found in a room occupied by a campaigner for Lyndon LaRouche, a candidate for the 1980 Democratic Presidential nomination.

[1] by May 1980, Gallen's attention to politics and administrative work in the state capital caused him some personal financial difficulties, and he had to close his failing automobile dealership.

He called the spending plan "fundamentally and fatally flawed" and told legislators that a budget, more than any other government document, spells out the state's "level of compassion, its sense of justice and its concern for equity."

[3][13] Roy served as acting governor, the first woman to do so, for the final days of Gallen's term until Sununu was sworn in to office on January 6, 1983.