Mentioning his 1886 donation of the Kneller portrait (regarded at the time as by an unknown artist), Alison Inglis and others (2018) describe Litton as a “prominent colonist,” and note that he was a Fellow of the Royal Geographical Society of Australasia (FRGSA).
Further information on him seems to be scanty, but he is documented as having founded the Historical Society of Australasia in 1885, and edited several volumes of its Transactions (1885-6, 1891). He appears to have been of Irish heritage.
See AR 1889, p.43 (describing Litton as FRGSA); and Alison Inglis & others, “British and Australian portraits at the National Gallery of Victoria,” Art Journal of the NGV vol.56 (2018): available online via NGV catalogue
For Litton’s biographical details, as given above, see Bernard Burke & others, A genealogical and heraldic history of the landed gentry of Ireland, London, 1912, p.408 (available via Google Books). For his role as founder of the Historical Society of Australasia, see e.g. Kerrie Round, “Celebrating the Past: the Growth of Amateur History in South Australia,” PhD thesis, University of Adelaide, 1995 (available online); and for his edited Transactions, see e.g. https://trove.nla.gov.au/work/5531231? (all websites noted accessed 6 May 2020)