Kim Thorson was born on March 2, 1932 at Macoun, Saskatchewan to Miles and Ethel Mary Thorson. He attended school in the Macoun district. Thorson earned Bachelor of Arts and Bachelor of Science in Agriculture degrees from the University of Saskatchewan. Prior to entering politics, Thorson was a farm economist with the Government of Saskatchewan. In December 1955, Thorson became the youngest candidate ever to contest a provincial election in Saskatchewan.
Thorson was first elected to the Saskatchewan Legislature in 1956 and served as a Co-operative Commonwealth Federation (CCF) member for the Souris-Estevan constituency until he was defeated in the 1960 general election by Ian Hugh MacDougall of the Liberal Party. Thorson returned to university and earned a Bachelor of Laws degree from the University of Saskatchewan, and was admitted to the bar in August 1964. He was a practising lawyer in Estevan when he was re-elected in a 1971 by-election. Thorson served as the Member of the Legislative Assembly for the Souris-Estevan constituency until 1975.
Thorson served in the Allan Blakeney Government as Minister of Mineral Resources (1972-1973) and Minister of Industry and Commerce (1972-1975). He was also Minister Responsible for Saskatchewan Power Corporation; Saskatchewan Economic Development Corporation; Liquor Licensing Commission; Liquor Board; and was Agent General. Thorson retired from political life in 1975.
Thorson resumed practising law full-time in Regina where he became a partner in the law firm of Griffin, Beke, Thorson, Olive & Waller. He later held partnership in the firms of Griffin Beke Thorson Goudie; Griffin Beke Thorson; Griffin Thorson Maddigan; and Hardy & Thorson. In the mid-1990s, Thorson moved to Weyburn and continued the partnership of Hardy & Thorson, and later formed Thorson & Horner. Thorson served on the Boards of Directors of IPSCO (1980-1992) and Cameco (1992-1998). He also served as Chairman of the T.C. Douglas Centre in Weyburn, and as a member of the Rotary Club of Weyburn and the Weyburn and District United Way.
Kim Thorson married Myrtle Lipsett on October 12, 1957. They have three children: Eric, Janet and Vanessa. Thorson continues (2010) to reside in Weyburn.