Born in the city of Idaho Falls, Crapo is a graduate of Brigham Young University and Harvard Law School. He practiced law in his home city throughout the 1980s, while maintaining an active role in local Republican politics. His brother Terry Crapo was majority leader in the Idaho House of Representatives and a growing political figure until his death from leukemia in 1982. Mike Crapo, prompted by his brother's death, successfully ran for the Idaho Senate in 1984. He became Senate President pro tempore from 1988 to 1992, in which position he served as Acting Governor of Idaho for 12 hours in January 1989.
Crapo was elected to Congress in 1992, representing Idaho's 2nd congressional district in the United States House of Representatives. After three terms in the House he was elected to the U.S. Senate in 1998. He was re-elected with no Democratic opposition in the 2004 election, a rarity in the Senate. He was again re-elected in 2010.