Associated with the South Australian Museum, he is recognised for his extensive surveys and research on mammals in Central Australia and systematically documenting the knowledge of the Indigenous peoples of the region.
Finlayson was injured in a series of laboratory accidents during his early career, including an explosion in 1913 resulting in the loss of his left hand and right eye.
[a][2] In 1917 Finlayson joined a committee examining the properties of Xanthorrhoea (grass trees) resin, which had been exported in large quantities to Germany—before the outbreak of war between the nations—and suspected to have been used in the manufacture of explosives.
[2] The explorations and field research Finlayson undertook were self-funded, among them four significant expeditions to remote and arid regions during austral summers of the early 1930s.
A variety of records and specimens of mammals were obtained on these journeys, but Finlayson took an especial interest in larger marsupials known locally as toolache (Macropus greyi), the brusher and ti tree wallaby.
[2] He made extensive use of the zoological information provided by the Aboriginal peoples of central desert regions, documenting their intimate knowledge of the species that still inhabited, or had disappeared from, their local environment.