 At the 1929 general election Stewart was elected to Stormont for the seat of East Tyrone, which he held until his death in 1964.Following the death of Joseph Devlin, Stewart was elected to Westminster at the 1934 Fermanagh and Tyrone by-election, but he stood down at the following year's general election.In 1958 Stewart became the Chairman of the Nationalist Party at Stormont, a position he retained until his death.