Mortensen sat in the municipal council of Skørping Municipality from 2001 to 2007, and then sat in the newly formed Rebild Municipality's municipal council in 2007. In 2007 he was also elected into parliament.
On 19 November 2020 Mortensen was appointed Minister of Development and Nordic Cooperation.[2]
Other activities
Joint World Bank-IMF Development Committee, Member (since 2022)[3]
World Bank, Ex-Officio Member of the Board of Governors (since 2020)[4]