Dietzen was an attorney with the law firm of Larkin, Hoffman, Daly & Lindren, Ltd., of Bloomington, Minnesota, from 1978 to 2004, and with the firm of Richter, Wimberly, & Ericson in Spokane, Washington, from 1973 to 1977.[2] He also served as an attorney for Tim Pawlenty during his 2002 gubernatorial campaign.[3]
Dietzen joined the Minnesota Supreme Court on February 19, 2008.[1] He was appointed to the court by Pawlenty after the resignation of Justice Sam Hanson.[3] From December 15, 2004, to February 19, 2008, he served as a judge on the Minnesota Court of Appeals.[4] He was likewise appointed to that judgeship by Pawlenty and then elected to it in 2006.
In 2001 and 2004, Dietzen contributed $250 to the reelection campaign of Norm Coleman, with his last donation occurring almost a year before he became a judge.[5][6]
Dietzen retired from the Supreme Court on August 31, 2016, seven months before reaching the mandatory retirement age.[7]