Jumonville was born in the seigneury of Verchères, New France (now part of Quebec), the son of Nicolas-Antoine Coulon de Villiers, a French military officer. He began service with the French military at age 15 in his father's unit.
He served in the army during several conflicts with native groups in the western Great Lakes region where he was stationed with his father and several of his brothers. His father and one of his brothers were killed at Baie-des-Puants (present Green Bay, Wisconsin) during a battle with the Fox tribe. He was later promoted to Second Ensign and was stationed in Acadia during King George's War (a branch conflict of the War of the Austrian Succession).
In June 1754, Jumonville was posted to Fort Duquesne with his older half-brother Louis Coulon de Villiers. The French were building up military strength in the Ohio Country in response to incursions by British traders and settlers.
On May 23, 1754, Jumonville took command of a 35 man detachment from the fort and headed southeast. The exact nature of Jumonville's mission has been the subject of considerable debate both at the time and up to the present day. Officially, his mission was to scout the area south of the fort. The French would later claim that he was a diplomat on a peaceful mission to deliver a message to the British. The British contended that he was sent to spy on their garrison at Fort Necessity and their road building project. Half King, the leader of a band of Mingos allied to the British, believed he was planning an ambush.
On May 27, 1754, a group of Native American scouts discovered Jumonville's party camped in a small valley (later called Jumonville Glen) near what is now Uniontown, Pennsylvania. Half King went to Washington and pled with him to attack the French encampment, claiming it was a hostile party sent to ambush them.
Washington took a detachment of about 40 men from Fort Necessity and marched all night in a driving rain arriving at the encampment at dawn. What happened next, like so much about the incident, is a matter of controversy. The British claimed the French discovered their approach and opened fire on them. The French claimed the British ambushed their encampment. In either event, the battle lasted little more than 15 minutes and was a complete British victory. Ten French soldiers were killed and 21, including Jumonville, who was wounded, were captured.
Washington treated Jumonville as a prisoner of war and extended him the customary courtesies due a captured military officer. Washington attempted to interrogate Jumonville but the language barrier made communication difficult. During their conversation however, the Seneca Half King Tanaghrisson walked up to Jumonville and without warning struck him in the head with a tomahawk killing him.
Why the Half King did this has never been clear. He had been kidnapped by the French and sold into slavery as a child. He was also a representative of the Iroquois Confederacy, which stood to lose its authority over other Indian peoples in the Ohio River Valley if the French were able to assert their control. (For a detailed discussion, see Fred Anderson, Crucible of War: The Seven Years' War and the Fate of Empire in British North America 1754-1766 (2001).)
When word reached Fort Duquesne about the incident, Jumonville's half brother, Captain Coulon de Villiers, vowed revenge. He attacked Washington and the garrison at Fort Necessity and forced them to surrender on July 3, 1754. In the surrender document, written in French, Coulon de Villiers inserted a clause describing Jumonville's death as an "assassination". Washington, who did not speak French, signed the document. The assassination of the French diplomat and revered soldier Jumonville would later be used as propaganda by the French against the war crimes of Washington and the British, during the conflict.
Washington was heavily criticized in Britain for the incident. British statesman Horace Walpole referred to the controversy surrounding Jumonville's death as the "Jumonville Affair" and described it as "a volley fired by a young Virginian in the backwoods of America [that] set the world on fire."