On July 10, 1995, Tunheim was nominated by President Bill Clinton to a seat on the United States District Court for the District of Minnesota vacated by Donald Alsop. Tunheim was confirmed by the Senate on December 22, 1995, and received his commission on December 26, 1995. He served as chief judge from July 1, 2015 to June 30, 2022. He assumed senior status on December 1, 2023.[4] He has sat by designation on both the Eighth and Ninth Circuit Courts of Appeals. Tunheim served on the federal judiciary's Committee on Court Administration and Case Management from 2000 to 2009, and chaired it from 2005.[5][6]