Following resignations from Corbyn's shadow cabinet after the 2016 EU referendum, Lewis was appointed as shadow defence secretary. In September 2016, at the Labour Party's 2016 Conference, when Lewis was preparing to give his first speech as shadow defence secretary, a section of his speech announcing that he "would not seek to change" Labour's current policy on nuclear weapons was changed by Corbyn's communications advisor Seumas Milne. Lewis was informed of the change by a post-it note. A month later, Corbyn removed Lewis from the defence brief, replacing him with Nia Griffith. Lewis was then appointed as shadow business secretary. The move was viewed as a tactical demotion.