Thorson was born in Eau Claire, Wisconsin, and his family moved to Montana when he was 12 years old. In 1930, Thorson graduated with a degree in journalism from the University of Montana in Missoula, Montana.

In the early 1940s, Thorson played Charles Meredith in Midstream on radio, replacing Hugh Studebaker when Studebaker had health problems. He starred in a later version (1949-1952) of the radio series, I Love a Mystery, as Jack Packard, alongside Jim Boles as Doc and Tony Randall as Reggy. His other radio parts included the title roles in The Tom Mix Ralston Straightshooters and Dr. Paul and Bart Friday in Adventures by Morse. He was also a member of the cast of Family Skeleton. In 1955, he began portraying Paul Barbour on the radio version of One Man’s Family after having had the same role in the TV version of the program.