Adams entered state politics as a Republican legislator (1941–44; Speaker of the House, 1944). He served a term in the United States House of Representatives (1945–47), making a failed effort to capture the 1946 Republican gubernatorial nomination in New Hampshire. He lost to incumbent Charles M. Dale; he later won this office in 1948.
When Adams took office as governor, New Hampshire was suffering post-war recession. He called for frugality and thrift in both personal and state expenditures. Retirees were (and are) a significant part of New Hampshire's population; Adams called for increased state aid for the aged, and for legislation which would enable the state's seniors to qualify for Federal Old Age & Survivors Insurance. In 1950 he formed a Reorganization Committee to recommend changes in state operations, and he called for the legislature to act on the recommendations.
Adams's clipped New Hampshire twang and calls for frugality made him a virtual poster boy for Republican balanced budget values of the time. He served as chairman of the U.S. Conference of Governors (1951–52), and was then asked to be White House Chief of Staff for the new Republican president, Dwight D. Eisenhower. He was the first person in this position to enjoy the explicit title of "Chief of Staff."