He worked as a microbiologist in
Western Australia and
New South Wales for several years. He was appointed as a full Professor of
Pathology at the
University of Adelaide, and taught generations of students. Cleland was elected President of the
Royal Society of South Australia 1927–1928, and again in 1941. He became a member of the
Royal Australasian Ornithologists Union (RAOU) in 1902, and served as its President 1935–1936. In 1934–35, he published a two-volume monograph on the fungi of South Australia, one of the most comprehensive reviews of Australian fungi to date. Along with
Charles Duguid and
Constance Cooke, he was a board member of South Australia's
Aborigines Protection Board after its creation in 1940, established by the
Aborigines Act Amendment Act (1939) and "charged with the duty of controlling and promoting the welfare" of Aboriginal people. Cleland led a
University of Adelaide anthropological expedition to
Nepabunna Mission in the northern
Flinders Ranges in May 1937, whose members included
Charles P. Mountford as
ethnologist and
photographer, botanist
Thomas Harvey Johnston, virologist
Frank Fenner, and others. Cleland was the pathologist on the infamous
Taman Shud Case, in which an unidentified man was discovered dead on a beach 1 December 1948. While Cleland theorised that the man had been poisoned, he found no trace of it. The man was never identified. Cleland became increasingly interested in wildlife conservation and served as commissioner of the
Belair National Park in 1928 and as chairman in 1936–65. He chaired the
Flora and Fauna Handbooks Committee of South Australia, and with them oversaw the production of a series of descriptive biological manuals, and other books related to flora, fauna and geology. ==Legacy and honours==