In 1961, at the age of 46, Garnett was appointed Headmaster of
Geelong Grammar School in
Victoria, Australia and he and his family made what was to be a permanent move to Australia. He was the headmaster when
Prince Charles spent two terms at Geelong Grammar School. Garnett was a keen amateur ornithologist and joined the
Royal Australasian Ornithologists Union (RAOU) in 1964. In 1974, upon his retirement from Geelong Grammar, he became secretary of the RAOU and served in that position until 1980. As secretary he bore the brunt of the administrative load of a body undergoing major change as it evolved from what had become largely a birdwatching club into a scientific conservation organisation undertaking ventures such as the
Atlas of Australian Birds project. From 1980 to 1997 he also wrote a regular column for
The Age, published in
Melbourne. In 1984 Garnett contributed to the government's project to rejuvenate Victoria's country botanic gardens, and in the early 1990s successfully advocated the establishment of an independent board for the
Royal Botanic Gardens, Melbourne. In 1996 he was awarded the Medal of the
Order of Australia (OAM) for contributions to horticulture. ==Publications==