He was returned to the House of Commons in 2015 with an increased majority of 20,761. Following the European Union membership referendum on 23 June and David Cameron's resignation as Prime Minister, Smith was one of six MPs who led the leadership campaign on behalf of the Home Secretary, Theresa May. After May became Prime Minister on 13 July 2016, four days later Smith was appointed Vice-Chamberlain of the Household, a senior position within the Government Whips' Office. He served as Deputy Chief Whip to Gavin Williamson from June 2017 to November 2017 and then, on 2 November 2017, he was appointed Chief Whip of the House of Commons.