He wrote classic papers on the birds of the Red Sea, Nigeria, the Gold Coast, Indonesia, Borneo, Ecuador and Iraq.
[1] In Australia, Marchant was immediately involved in organised ornithology through the Royal Australasian Ornithologists Union (RAOU) where he was a strong force for what he perceived to be necessary reform.
[1] Following a 12-year stint as Emu Editor, he turned his attention to a new project, a comprehensive handbook of Australian birds, an endeavour which expanded in scope to become the Handbook of Australian, New Zealand and Antarctic Birds (HANZAB) of which he was the editor-in-chief of the first two volumes.
His contribution to Australian ornithology was recognised by his being made an Honorary Member in the General Division of the Order of Australia (AM) in 1994, and by being awarded the RAOU's John Hobbs Medal in 1997.
Marchant died in August 2003, at a nursing home between the New South Wales towns of Moruya and Narooma.