He was a member of federal parliament from 1963 to 1972, representing the Liberal Party, and served as Minister for the Navy in the McMahon government.

He was an ordained Presbyterian minister and prior to entering parliament served as the general secretary of the Australian division of the World Council of Churches.

Mackay was born in Brighton, South Australia and educated at Adelaide Technical High School.

He was ordained and inducted to the Merbein-Wentworth parish on 1 July 1952, demitted 14 June 1954 and from 1954 until 1956, he was the Australian General Secretary for the World Council of Churches.

[3] Mackay was made a Member of the Order of Australia in 1986 for "services to the community particularly in the fields of religion, education and politics.