Green’s Dictionary of Slang

(Aus.) a released convict.

1869		Australasian (Melbourne) 17 July 8/5: The derivation of Sydney-sider and Derwenter, &c is obvious.
1880		‘Erro’ Squattermania 61: It’s a quiet little place [...] with a good many Derwenters in it (ticket-of-leave men from Tasmania); they are generally called old hands out here.
1884		‘Rolf Boldrewood’ Old Melbourne Memories 140: An odd pair of sawyers, generally ‘Derwenters,’ as the Tasmanian expirees were called.
1890–1904		Farmer & Henley Sl. and Its Analogues.