Gerald Colin McKellar was born in Gulgong and educated at Gilgandra (NSW). In 1936, he joined the Commonwealth Military Forces as a Lieutenant, 6th Light Horse Regiment and was promoted to Captain and then Major in September 1942. The same month, he enlisted in the 2nd Australian Imperial Force and served with 26 Motor Regiment and with 1 Australian Ordnance White Park. His appointment was terminated on 3 April 1946.

After World War II, McKellar became Chairman of the Lawson Council (representing the Country Party), a position he held for ten years before becoming Chairman of the Electorate of Castlereagh and then Chairman of the Country Party in NSW (1957-58). In the same period he was also Chairman of Gilgandra Newspapers Pty Ltd for two years and a Director of the Dubbo Primary Producers' Board for four years.

In 1958, McKellar was elected as a Senator for NSW to fill a casual vacancy caused by the death of W P Ashley. He retained the seat until his own death in 1970. McKellar held only one portfolio during his Parliamentary career, as Minister for Repatriation (1964-69) in the Menzies, Holt and Gorton Governments, although he also acted as Minister for Social Services on several occasions (1966-68). He was a member of the Senate Standing Committee on Regulations and Ordinances (1959-62), the Joint Committee of Public Accounts and Audit (1961-62), the Senate Committee on Standing Orders (1962-64) and was Temporary Chairman and then Chairman of Committees for the Senate (1961-64). 

Senator McKellar made several official visits overseas, including as a member of the Parliamentary delegation to the first meeting of the Legislative Council for Papua and New Guinea in its new Council Chambers (October 1960) and as a member of the Australian delegation to the 17th Session General Assembly of the United Nations in New York (1962). He died in Sydney on 13 April 1970 while attending the annual dinner of the NSW Graziers Association.

Sources:

Parliamentary Handbook 1968, pp 161-2; 1971, p 408
Who's Who in Australia 1968, p 568