Elworthy was made Chief of the Air Staff on 1 September 1963. As Chief of the Air Staff, he worked closely with Secretary of State Denis Healey implementing the cancellation of the TSR-2 strike aircraft and the HS681 military transport aircraft programmes. He was promoted to Marshal of the Royal Air Force on 1 April 1967 and became Chief of the Defence Staff on 4 August 1967. In this role he oversaw the evacuation from Aden in November 1967 and had to respond to the growing crisis in Northern Ireland in the late 1960s. He retired in April 1971.