He ran as the 2nd Alliance Party candidate in East Antrim from the 1996 Northern Ireland Forum to the 2007 Assembly Elections, alongside Seán Neeson but was not elected until the 2011 Assembly Elections; where he inherited Seán Neeson's seat following his retirement.
Stewart is a Trustee of the NI Cancer Charity, OG Cancer NI having been diagnosed with Oesophageal Cancer in July 2019 and underwent major surgery later that year.
Outside political life, he is a retired member of the Northern Ireland Public Service Alliance trade union and the Greenisland Presbyterian Church where he and his wife Sandra are both Elders. He is a former long-serving member and Chair of the Boards of Governors of Carrickfergus Central and Silverstream Primary Schools. Stewart is a Winston Churchill Fellow, having completed his fellowship on: ‘How to create and sustain a small business’. He travelled to the New England States of the United States for his fellowship in 1999. Prior to his election to the NI Assembly, he worked as Arbitration Secretary at the Northern Ireland Labour Relations Agency.