Wallace served as a Parliamentary Private Secretary to the Justice Secretary, and later Minister without Portfolio, Ken Clarke from 2010 to 2014. Wallace was a whip from July 2014 to May 2015. He served as Parliamentary Under-Secretary of State for the Northern Ireland Office under David Cameron from 2015 to 2016. He served under Prime Minister Theresa May as Minister of State for Security and Economic Crime at the Home Office from 2016 to 2019. A supporter of Boris Johnson's leadership bid, Johnson appointed Wallace as Secretary of State for Defence after he was appointed Prime Minister.