Stewart was a candidate in the 2019 Conservative leadership election, announcing his intention to stand in an interview in "The Times." His candidacy was not initially taken seriously, with a piece in the "New Statesman"'s diary stating that he had a single supporter: himself. As "The Guardian" noted: "his campaign benefited at the start from low expectations, and for days leading up to the first vote his tally of supporters was in single figures. When he met the threshold he looked like the insurgent because so many had assumed he would be knocked out".