In June 2015, he was elected to the Chair of the Commons Defence Select Committee by 314 votes to 242, and in July 2017 he was re-elected to this position, in the new Parliament, by 305 votes to 265. Having supervised more than 30 Inquiries, during the 2015–17 and 2017–19 Parliaments, Lewis made it known in January 2020 that he would not seek re-election to chair the Defence Committee for a third time, as "It is better to stop while people wish you to carry on, than to carry on until people wish you to stop!"