Kirby worked for Western Surety Company from 1977-92 as corporate secretary and senior claim counsel.
He entered the race after John Thune declared he would not run, but lost the election to Mike Rounds.
When Thune passed on the race in order to challenge Senator Tim Johnson, state Attorney General Mark Barnett and Kirby quickly became candidates.
Rounds' positive image and extensive knowledge of state government won him many supporters who were alienated by the front-runners.
On the day of the primary election, Rounds won a stunning victory, with 44.3% of the vote to Barnett's 29.5% and Kirby's 26.1%.