Upon joining the House of Commons, Stewart was elected a member of the Foreign Affairs Select Committee, serving until 2014. During his tenure on the committee, he was also chair of the trans-Atlantic group Le Cercle but did not declare his membership. Stewart also served as the chair of the APPG for Mountain Rescue and the APPG for Local Democracy, and was an officer of the APPG for Rural Services. He was elected chair of the Defence Select Committee in May 2014. He left these positions upon his appointment as environment minister.