Living in Portrush, Stewart joined the Democratic Unionist Party (DUP), and first stood for Coleraine Borough Council for the party in the Skerries ward, at the 1985 Northern Ireland local elections. Although he was unsuccessful, he was narrowly elected at the following election, in 1989, and then topped the poll in 1993. At the Northern Ireland Forum election in 1996, he stood in East Londonderry, and was elected from second place on the DUP list.
Following the 2005 Northern Ireland local elections, in which Stewart was again re-elected, he was accused of electoral fraud. He was subsequently convicted of taking fifteen electoral votes from a care home and using them to vote for himself. He admitted the charges and resigned from both his party and the council, and was sentenced to four months in prison. During his trial, he punched a press photographer, for which he was fined £300. The subsequent council by-election was won by the Alliance Party, which has held the seat ever since.
- "Local Government Elections 1985 - 1989: Coleraine", Northern Ireland Elections
- "Coleraine Borough Council Elections 1993-2011", Northern Ireland Elections
- "East Londonderry", Northern Ireland Elections
- "Council elects new mayor Archived 19 May 2014 at the Wayback Machine", Coleraine Borough Council
- Northern Ireland Yearbook 2004, p.223
- "Ex DUP councillor jailed for electoral fraud", RTÉ, 17 November 2006
- "Vote to replace shamed ex-mayor", BBC News, 25 October 2006
- "Former mayor guilty of assault", BBC News, 22 May 2007
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