Following the double dissolution of 11 April 1974 and subsequent federal election, O'Byrne was elected President of the Senate on 9 July 1974. He held this office until the Dismissal of the Whitlam government on 11 November 1975. Senator Robert Ray said of O'Byrne's time as President of the Senate "Justin presided over the Senate during one of the most tumultuous and still controversial periods in Australian politics. The fact that there was not one dissent from his rulings, nor any vote of no confidence, is a testament to his performance and the high regard in which he was held by those on both sides of the chamber."