[4] [5] During his time at Alice Springs he became involved with Aboriginal Australians and in 1894 assisted the Horn Scientific Expedition to Central Australia, soon after which he met Walter Baldwin Spencer.

After witnessing and documenting the Engwura festival – a series of public and restricted ceremonies performed by Arrernte people men in 1896 – they worked together to write The Native Tribes of Central Australia (1899).

[citation needed] Gillen was transferred from Alice Springs to Moonta in 1899, but in 1901 he was given leave by the South Australian government to join Spencer in an expedition which took them up to the Gulf of Carpentaria.

Gillen's final fieldwork endeavour with Spencer was to the old Peake station, South Australia, where they camped for a number of weeks gathering further information on Arabanna people for inclusion on their 1904 publication.

His wife, formerly Amelia Besley of Mount Gambier[1] (and step-sister to "Pado" Byrne, telegraph master and scientist at Charlotte Waters for 50 years), three daughters and two sons survived him.