| Honorific-Prefix: | The Hon. |
| William Berrian Vail | |
| Constituency Mp: | Digby |
| Parliament: | Canadian |
| Predecessor: | Edwin Randolph Oakes |
| Successor: | John Chipman Wade |
| Term Start: | 1874 |
| Term End: | 1877 |
| Predecessor2: | John Chipman Wade |
| Successor2: | John Campbell |
| Term Start2: | 1882 |
| Term End2: | 1887 |
| Office3: | Member of the Nova Scotia House of Assembly for Digby County |
| Term Start3: | 1867 |
| Term End3: | 1874 |
| Birth Date: | December 19, 1823 |
| Birth Place: | Sussex Vale, Colony of New Brunswick |
| Death Place: | Dover, England |
| Party: | Liberal |
| Otherparty: | Nova Scotia Liberal Party |
| Relations: | Edwin Arnold Vail, brother |
| Cabinet: | Provincial: Provincial Secretary (1867-1874) Federal: Minister of Militia and Defence (1874-1878) |
William Berrian Vail, (December 19, 1823 - April 10, 1904) was a Canadian businessman and politician.
Vail was born in Sussex Vale, New Brunswick, the son of John Cougle Vail and Charlotte Hannah Arnold. In 1850, he married Charlotte Leslie Jones. He represented Digby County in the Nova Scotia House of Assembly from 1867 to 1874. He served in the province's Executive Council as provincial secretary. In 1874, he was elected to the 3rd Canadian Parliament as the Liberal Member of Parliament for Digby. From 1874 to 1878, he was the Minister of Militia and Defence under Alexander Mackenzie. He resigned because of a conflict of interest in the 1877 but returned to parliament in 1882 where he served as an opposition MP until he lost his seat once again in the 1887 general election. He died in Dover, England.
His brother Edwin Arnold Vail served in the New Brunswick assembly.