The colonies, in solidarity with the Province of Massachusetts Bay—which had been singled out for punishment by those acts in the wake of the Boston Tea Party—had organized a Congress to meet in September 1774.

In early September, General Thomas Gage, the royal governor of Massachusetts, had removed gunpowder from a powder magazine in Charlestown (in a location now in Somerville), and militia from all over New England had flocked to the area in response to false rumors that violence had been involved.

[4] In early 1775, Virginians began to organize militia companies and seek out military supplies (weapons, ammunition, and gunpowder) to arm and equip them.

On April 19, Lord Dunmore quietly brought a company of British sailors into Williamsburg and quartered them in the governor's mansion.

Dunmore then ordered Captain Henry Collins, commander of HMS Magdalen, to remove the gunpowder from the magazine in Williamsburg.

Dunmore demurred, stating that he was moving the powder as protection against its seizure during a rumored slave uprising, and would eventually return it.

After a second crowd was convinced to disperse by Patriot leaders, Dunmore reacted angrily, warning on April 22 that if attacked, he would "declare Freedom to the Slaves, and reduce the City of Williamsburg to Ashes.

Henry dispatched a small company to the home of Richard Corbin, who was the deputy collector of the royal revenue in Virginia, in a bid to force him to pay for the powder from Crown revenue in his possession; the remainder of the Hanover County militia, numbering about 150, marched toward Williamsburg, arriving about 15 miles (24 km) away on May 3.

[12][14] Although his family briefly returned to Williamsburg on May 12 as a sign of good faith, relations between Dunmore and the House of Burgesses continued to deteriorate.

The subsequent outrage by the local population proved to be the final act of the Gunpowder Incident, leading Governor Dunmore to flee the city to a British warship and declare the Commonwealth of Virginia in a state of rebellion.