Hjelm was appointed to the Maine District Court in 1992 and to the Maine Superior Court in 1998. He was reappointed to the Superior Court in 2005 and 2012. On May 7, 2014, Hjelm was nominated by Paul LePage to be an associate justice of the Maine Supreme Judicial Court.[1] On August 1, 2014, Hjelm was sworn in by Governor Paul LePage as an associate justice.[3] On September 20, 2019, Hjelm announced his intention to retire upon the confirmation of his successor.[4][5] He retired in December 2019.[6] He was later sworn in as an Active Retired Justice of the Maine Supreme Judicial Court.[7]