In 2002, he was elected to Seanad Éireann as a Fine Gael candidate for the Industrial and Commercial Panel. He stood down as a member of Longford County Council when legislation was introduced prohibiting serving members of the Oireachtas from being members of local authorities, and was succeeded by his brother, Larry. He was first elected to Dáil Éireann at the 2007 general election for Longford–Westmeath.
He served as the party deputy spokesperson on Environment, with special responsibility for Heritage from 2007 to 2010. In October 2010, he was appointed as deputy spokesperson on Environment with special responsibility for Local and Community Development.
During campaigning ahead of the 2016 general election, Gardaí gave Bannon a lift after he became involved in a dispute while canvassing in the Creevaghbeg estate area in Ballymahon, County Longford. An associate of Bannon was reported to have stolen election leaflets belonging to a rival candidate from local letter boxes.[4]