Garnsey was educated at the University of Sydney,[3] winning a Rhodes Scholarship in 1931, and at New College, Oxford.
[5] His first post was as a curate at the University Church of St Mary the Virgin, Oxford.
From 1948 until his consecration to the episcopate in 1959, he was headmaster of Canberra Grammar School.
In Gippsland, Garnsey took a leading role in promoting women for church leadership and was "in the forefront of radical thinking in the areas of women's ministry and ecumenical partnerships".
[citation needed] In 1966 the synod of Victoria appointed him to chair a commission on the ministry of deaconesses.