A highly decorated World War II veteran, Thomson served three terms in Wyoming's only U.S. House seat.

He had been admitted to the bar in 1941 and commenced the practice of law in Cheyenne in February 1946; he was a delegate to the 1952 Republican National Convention in Chicago and was a member of the Wyoming House of Representatives from 1952 to 1954.

Thomson was elected as a member of the Republican Party to the Eighty-fourth, Eighty-fifth, and Eighty-sixth Congresses and served from January 3, 1955, until his death.

[2][3][4] He did not seek renomination to the Eighty-seventh Congress, but was elected to the United States Senate on November 8, 1960, for the term commencing January 3, 1961.

Democratic Governor John J. Hickey appointed himself to the seat but was defeated in a 1962 special election to serve out the term by Republican Milward L. Simpson.