In 1901 he left the bank to become General Manager of the Rhodesia Exploration and Development Company, which sought to build up property.
[1] Elected as a Member of the Southern Rhodesian Legislative Council in 1911 for the Western District, in 1918 Mitchell retired from business and thereafter devoted himself to politics where he was a supporter of the Rhodesia Party and of responsible government within the colony of Southern Rhodesia.
[2] With the grant of responsible government in 1923, Mitchell stood at the first election to the Southern Rhodesian Legislative Assembly for the seat of Bulawayo South, but was unsuccessful.
He was appointed to the Government of Southern Rhodesia on 1 November 1930 as Minister of Mines and Public Works.
[2] When Howard Moffat resigned in 1933, Mitchell was chosen as the new Premier and chose to change the job title to Prime Minister.