William Berrian Vail, PC (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