On 13 May 1965, he became Deputy Premier, Minister for Education and Minister for Science under the newly elected Liberal Party Premier Robert Askin, in NSW's first non-Labor government in 24 years. In later years, he also held portfolios as Minister for Local Government, Minister for Highways and Minister for Tourism. For several months in 1968 and 1972, he was Acting Premier and Treasurer in Askin's absence. He remained as Deputy Premier for most of 1975 under Tom Lewis after Askin's retirement that year.