Shallenburger was a member of the House of Representatives from 1987 to 1998, serving as Speaker from 1995 to 1998. He was then Treasurer from 1999 to 2003, at which time he was succeeded by Lynn Jenkins, who later became a member of the United States House of Representatives. In 2002, Shallenburger ran for Governor of Kansas, losing to Kathleen Sebelius, who later became United States Secretary of Health and Human Services. He serves as the Legislative Director for the Office of Governor Sam Brownback.