Lawrence Washington's service as adjutant general of the Virginia militia inspired his half-brother George to seek a commission. Virginia's lieutenant governor, Robert Dinwiddie, appointed George Washington as a major and commander of one of the four militia districts. The British and French were competing for control of the Ohio Valley. While the British were constructing forts along the Ohio River, the French were doing the same—constructing forts between the Ohio River and Lake Erie.

In October 1753, Dinwiddie appointed Washington as a special envoy. He had sent George to demand French forces to vacate land that was being claimed by the British. Washington was also appointed to make peace with the Iroquois Confederacy, and to gather further intelligence about the French forces. Washington met with Half-King Tanacharison, and other Iroquois chiefs, at Logstown, and gathered information about the numbers and locations of the French forts, as well as intelligence concerning individuals taken prisoner by the French. Washington was given the nickname Conotocaurius (town destroyer or devourer of villages) by Tanacharison. The nickname had previously been given to his great-grandfather John Washington in the late seventeenth century by the Susquehannock.

Washington's party reached the Ohio River in November 1753, and was intercepted by a French patrol. The party was escorted to Fort Le Boeuf, where Washington was received in a friendly manner. He delivered the British demand to vacate to the French commander Saint-Pierre, but the French refused to leave. Saint-Pierre gave Washington his official answer in a sealed envelope after a few days' delay, as well as food and extra winter clothing for his party's journey back to Virginia. Washington completed the precarious mission in 77 days, in difficult winter conditions, achieving a measure of distinction when his report was published in Virginia and in London.