While still a law student, Kline ran for U.S. Congress in 1986. Kline won the Republican primary election but was defeated in the general election by the incumbent, Democrat Jim Slattery. In 1992, Kline won election to the Kansas House of Representatives, where he represented the 18th District. which included Shawnee. There, he chaired the House Appropriations Committee and was a member of several oversight committees. He was a member of the advisory committee for Kansas Senator Bob Dole's 1996 presidential campaign. Kline remained in the Kansas House until 2000, when he ran for election to the United States House of Representatives, seeking the Third District seat held by Democratic Congressman Dennis Moore. Although Kline won the Republican primary, he lost the general election to Moore, 184,050 to 145,542 votes, 54.8% to 43.3%.