He became a member of Kirkintilloch Community Council in 2003 and stood as Labour's candidate for the Chapelton Ward of East Dunbartonshire Council in 2003 where he was defeated by the Liberal Democrat candidate, Fiona Callison.
In 2005, Stewart MacDonald gave a speech on behalf of Cumbernauld, Kilsyth and Kirkintilloch East Constituency Labour Party to the Scottish Labour Party Conference on the minimum wage.