| Honorific-Prefix: | The Honourable |
| Joseph Leonard O'Brien | |
| Order: | 21st |
| Office: | Lieutenant Governor of New Brunswick |
| Predecessor: | David Laurence MacLaren |
| Successor: | John B. McNair |
| Term Start: | June 5, 1958 |
| Term End: | June 9, 1965 |
| Governor General: | Vincent Massey Georges Vanier |
| Premier: | Hugh John Flemming Louis Robichaud |
| Constituency Mp2: | Northumberland |
| Parliament2: | Canadian |
| Predecessor2: | John Patrick Barry |
| Successor2: | John William Maloney |
| Term Start2: | 1940 |
| Term End2: | 1945 |
| Office3: | Member of the Legislative Assembly of New Brunswick for Northumberland |
| Term Start3: | 1925 |
| Term End3: | 1930 |
| Office4: | Speaker of the Legislative Assembly of New Brunswick |
| Predecessor4: | Allison Dysart |
| Successor4: | Frederick C. Squires |
| Term Start4: | 1926 |
| Term End4: | 1930 |
| Birth Date: | 10 November 1895 |
| Birth Place: | South Nelson, New Brunswick, Canada |
| Spouse: | Kathleen O'Leary |
| Party: | National Government |
Joseph Leonard O'Brien (November 10, 1895 - June 18, 1973) was a Canadian politician and businessman. Born in South Nelson, New Brunswick, he was a member of the Legislative Assembly of New Brunswick from 1925 to 1930 and was Speaker of the Assembly. By profession he was a lumber merchant, operating a small sawmill in South Nelson.
In 1940, he was elected to the House of Commons of Canada for the riding of Northumberland. A member of the National Government, he was defeated in 1945. In 1958, he was appointed the 21st Lieutenant Governor of New Brunswick and served until 1965.
He purchased Beaubears Island, New Brunswick in 1920 for the sum of $1.00. A monument stands in the national park on the island in his honour.
His remains rest at Malcolm Cemetery of St. Patrick's Church located in Nelson-Miramichi, Miramichi, New Brunswick, Canada.