He was the 14th and 16th state treasurer of Wisconsin—he was removed from office by the governor in 1904 during his first term and then won election to return to office later that year.
He also served in the Wisconsin State Senate, representing the north side of the city of Milwaukee.
He was a member of the Wisconsin State Senate and the Register of Deeds of Milwaukee County before serving as Treasurer of Wisconsin from 1903 to 1904 and again from 1905 to 1907.
Additionally, he was a member of the Republican State Central Committee from 1900 to 1903.
On August 30, 1904, the Governor of Wisconsin Robert M. La Follette removed Kempf from office and appointed Thomas M. Purtell acting treasurer.