Blackburn was born in Melbourne in 1914 and began his ministry as a home missionary at Beechworth Baptist church in 1934.
In 1947 Blackburn was appointed as the Baptist Union of Victoria's first full-time Youth Director, during which time he completed a BEd at the University of Melbourne.
He served in the capacity of Editor of Sunday School Publications from 1949 to 1972, before returning to parish ministry at Syndal until his retirement in 1986.
The Geoffrey Blackburn Library at Whitley College is named in his honour, and he was one of the inaugural inductees into the Camberwell Grammar School Gallery of Achievement.
Rowland Croucher described Blackburn as one of the four most admired Australian Baptists, alongside G. H. Morling, F. W. Boreham and Noel Vose.