Smyth became a Labour party organiser in 2003.[3] In 2008, he was appointed general secretary of the Scottish Labour Party, succeeding Lesley Quinn.[4] In September 2012, Scottish Labour announced that Smyth would step down from the position at the party's conference in the following month.
In 2007, Smyth was elected to Dumfries and Galloway Council, representing the Nith Ward. He was re-elected to this position in 2012.[5] In October 2013, a Labour/SNP coalition was formed on Dumfries and Galloway Council[6] when Smyth was appointed Chair of the Planning, Housing and Environment Committee.