Mitchell entered parliament as the United Australia Party member for Burwood after winning the seat at the 1938 state election. He won 51% of the vote and defeated the only other candidate, the incumbent member Gordon Jackett. Unusually, Jackett had also been endorsed by the UAP. This was indicative of the growing disunity and lack of organizational strength within the UAP. To forestall pre-selection ballots, the party's central committee, of which Mitchell was a member, had declared 11 metropolitan seats including Burwood to be "safe seats" and had endorsed multiple candidates. At the next state election in 1941, Jackett stood as an Independent "Nationalist UAP" candidate and defeated Mitchell who finished third with 28% of the vote behind Jackett and the Labor Party candidate, Albert Thompson. Thompson won a remarkable 38% of the vote due to the large statewide swing to Labor at the election. After an absence of 9 years, Mitchell again nominated for Burwood at the 1950 state election. He stood as an Independent and was easily defeated by Jackett who was the endorsed candidate of the Liberal Party. This was the last state election that Mitchell contested. He did not hold party, parliamentary or ministerial office.
