Denis T. O'Connor C.S.B. (26 February 1841 – 30 June 1911) was the Roman Catholic Archbishop of Toronto from 1899 to 1908 and the first Canadian born Archbishop of Toronto and the first Canadian head of the diocese since Michael Power.
O'Connor was born in Pickering, Ontario, attended St. Michael's College, Toronto, and professed as a member of the Congregation of St. Basil in 1860. He was ordained a Basilian priest in 1863 by John Joseph Lynch.
O'Connor became a theology professor at St. Michael's College in Toronto and Superior of Assumption College in Windsor, Ontario. O'Connor left his academic posting and was appointed Bishop of Diocese of London, Ontario in 1890 and finally as Archbishop of Toronto in 1899.
O'Connor's academic background made him a strong supporter of education. Under O'Connor, there was a drive for certification for Separate School teachers and he guaranteed an equal education for all Catholics. In Toronto, however, O'Connor refused to allow the Knights of Columbus to expand into his archdiocese on the grounds that there were already too many Catholic societies in existence.
He also served as Titular Archbishop of Laodicea in Syria from 1908 and made Archbishop Emeritus in 1911. Forced to resign due to his poor health (O'Connor suffered from Bright's Disease and diabetes), he died in Toronto in 1911. He is buried in a Basilian plot at Mount Hope Catholic Cemetery in Ontario. A Catholic High School in Ajax, Ontario is named for him.