[4] During the Second World War, he served in the Alaskan Theater as a lieutenant in the United States Naval Reserve from 1942 to 1946.

He also served as general counsel to a United States Senate committee in 1946; secretary to Senator Styles Bridges in 1947; counsel to the Joint Congressional Committee on Foreign Economic Cooperation from 1948 to 1949; attorney general of New Hampshire from 1953 to 1961; president of the National Association of Attorneys General in 1957; and as legislative counsel to the Governor of New Hampshire in 1961; member and chairman of several state legal and judicial commissions.

His attempts to investigate alleged communists as attorney general lead to the Supreme Court case Sweezy v. New Hampshire, which ruled against the state and Wyman on due process grounds.

The initial returns showed him defeating Democratic candidate John A. Durkin by 355 votes on election night.

Cotton resigned on December 31, 1974; Thomson appointed Wyman to the seat for the balance of the term ending January 3, 1975, to give him a leg up in seniority.

Durkin agreed, and the Senate declared the seat officially vacant on August 8, 1975, pending the new election.