Mortenson first ran for the South Dakota House of Representatives from District 24 in 2020. He won the primary in June 2020 and the general election on November 3, 2020. In 2021, Mortenson filed articles of impeachment against Attorney General Jason Ravnsborg,[3] and again in 2022,[4] leading to Ravnsborg's removal from office.[5]
In 2022, Mortenson was selected to serve as House Majority Leader by his Republican colleagues in the State House of Representatives.[6] He is the youngest Republican to serve as House Majority Leader in state history, and the first tribal member to lead a majority caucus.[7]