The Lyons-Seward Treaty of 1862 committed the United States and Britain to joint naval suppression of the Atlantic slave trade, closing a long-standing diplomatic gap.
Key Facts
- Treaty concluded
- April 7, 1862
- U.S. Senate ratification
- April 25, 1862 (unanimous)
- Ratifications exchanged
- May 25, 1862, in London
- U.S. negotiator
- Secretary of State William H. Seward
- British negotiator
- Ambassador Richard Lyons, 1st Viscount Lyons
By the Numbers
Location
Cause → Event → Consequence
Britain had long sought U.S. cooperation in suppressing the Atlantic slave trade, but American resistance to allowing Royal Navy search of vessels flying the U.S. flag had left a critical enforcement gap that slave traders exploited for decades.
U.S. Secretary of State William H. Seward and British Ambassador Richard Lyons negotiated a bilateral treaty concluded in Washington on April 7, 1862, and unanimously ratified by the U.S. Senate on April 25, 1862, committing both nations to active, cooperative suppression of the Atlantic slave trade.
With ratifications exchanged in London on May 25, 1862, the treaty removed the longstanding American objection to mutual naval search rights, enabling more effective joint interdiction of slave-trading vessels on the Atlantic and effectively closing the legal shelter that American registry had provided.
Political Outcome
Treaty ratified unanimously; both nations committed to joint suppression of the Atlantic slave trade with mutual naval search rights.