The Treaty of Washington was a treaty negotiated between Great Britain and the United States in 1871.

The treaty dealt with grievances stemming from the American Civil War (such as the Alabama claims and the Fenian raids) and cross-border issues with the newly-formed Dominion of Canada. Its negotiation helped to avert what some felt was an inevitable war between the two parties.

One of the negotiators on the British side was Canadian Prime Minister Sir John A. Macdonald. Although the treaty was signed in the name of the British Empire, Macdonald's presence established that the newly-formed Dominion of Canada would at least take part in settling foreign matters that affected it directly, especially with respect to dealings with the U.S.

In 1872, the U.S. was awarded $15,500,000 pursuant to the terms of the treaty. Compensation for the Fenian raids was not included. This greatly irritated Macdonald, but he nonetheless persuaded the Canadian House of Commons to ratify the treaty.

The scholar of international law John Bassett Moore has called this treaty "the greatest treaty of actual and immediate arbitration the world has ever seen."