Sir John Campbell Allen (October 1, 1817 – September 27, 1898) was from 1865–1896 a justice of the colonial and then provincial Supreme Court of New Brunswick, serving as Chief Justice of New Brunswick from 1875 to 1896.

He studied law in the office of John Simcoe Saunders.

In 1873, he gave the majority decision of the New Brunswick Supreme Court in Dow v. Black, a significant constitutional law case dealing with the federal-provincial division of powers.

He held that a provincial statute dealing with municipal taxation was unconstitutional.

However, his decision was overturned on appeal by the Judicial Committee of the Privy Council, at that time the court of last resort for the British Empire.