| Cornelius O'Brien | |
| Archbishop Of: | Archbishop of Halifax, Nova Scotia |
| Province: | Nova Scotia |
| See: | Halifax |
| Enthroned: | 1 December 1882 |
| Ended: | 9 March 1906 |
| Predecessor: | Michael Hannan |
| Successor: | Edward Joseph McCarthy |
| Ordination: | 8 April 1871 |
| Birth Date: | 1843 5, df=yes |
| Birth Place: | New Glasgow, Prince Edward Island |
| Death Place: | Halifax, Nova Scotia |
| Religion: | Roman Catholic |
Cornelius O'Brien (4 May 1843 - 9 March 1906) was a Canadian Roman Catholic priest, archbishop, and author of 39 books.
Born in New Glasgow, Prince Edward Island, the son of Terence O'Brien and Catherine O'Driscoll, O'Brien graduated from Urban College and in 1871 was ordained a priest.
In 1882, he was appointed Archbishop of Halifax, Nova Scotia. He followed Michael Hannan in this position. He established a Catholic high school (1888) and Holy Heart Seminary (1896), both in Halifax and helped to found the French-language Collège Sainte Anne (1890) in Pointe-de-l'Église, Nova Scotia.
In 1894 he delivered a eulogy for the Rt. Hon. Sir John Thompson, a former Premier of Nova Scotia and the first Catholic Prime Minister of Canada. From 1896 to 1897, he was president of the Royal Society of Canada.
He died in Halifax on 9 March 1906.He was buried in the Holy Cross Cemetery, Halifax.