John Gavan Duffy (15 October 1844 – 8 March 1917) was an Australian politician, member of the Victorian Legislative Assembly.

[1] Born in Dublin, Ireland to Charles Gavan Duffy (who would later serve as Premier of Victoria) and Emily McLaughlin, he arrived with his family in Melbourne in August 1859.

After some time on his father's farm he was articled as a clerk to a solicitor.

While continuing his legal practice, Duffy was elected to the Victorian Legislative Assembly as the member for Dalhousie in 1874; he was defeated in 1886 but returned in a by-election in 1887.

In 1889 he transferred to the new seat of Kilmore, Dalhousie and Lancefield, which he represented until 1904.