John C. O'Sullivan (1843 – 1887)[1] was a physician and politician in Ontario, Canada.
He represented Peterborough East in the Legislative Assembly of Ontario from 1875 to 1879 as a Conservative.
[2] He was born in Northumberland County, Canada West, of Irish descent, and was educated at Victoria University and Queen's University.
His election in 1875 was appealed but he won the by-election that followed later that year.
[3] In 1885, he was named president of the Irish National League branch in Peterborough.