William Pierce or William Leigh Pierce (c. 1740 – December 10, 1789) was an army officer during the American Revolutionary War and a member of the United States Constitutional Convention of 1787.
Little is known about Pierce's early life or background. He was born in York County, Virginia in 1753. He served in the Continental Army through most of the War of Independence. He was commissioned a captain in the 1st Continental Artillery Regiment on November 30, 1776. Due to failing health, he left the artillery to serve as an aide-de-camp to General John Sullivan during Sullivan's expedition against the Iroquois in 1779.
He returned to Virginia and attended the College of William and Mary, but in December 1780 he became an aide-de-camp to General Nathanael Greene. He served with Greene throughout the tumultuous southern campaign, and was recognized by Congress for his bravery at the Battle of Eutaw Springs on September 8, 1781. He received brevet promotion to major at the end of the war.
After his military service, Pierce sought to establish himself as a merchant in the West Indies. He eventually settled in Savannah, Georgia, and partnered with fellow officers Richard Call and Anthony Walton White. In 1783, he married Charlotte Fenwick, the daughter of a wealthy South Carolina planter. They had two or four sons: all but one died as children; the other was noted author William Leigh Pierce.
Pierce represented Chatham County in the Georgia State Legislature, which elected him to the Continental Congress in 1786, and to the Constitutional Convention the following year. At the Convention he kept notes on the proceedings and, more importantly, wrote character sketches of his fellow delegates. It is these sketches for which he is remembered. Pierce left the Convention in July to attend business matters and did not sign the Constitution.
Pierce had business troubles and substantial debts, and sought but did not receive appointment to a position in the federal government. He was unsuccessful in a bid for the United States House of Representatives in 1789. He was an original member and vice president of the Georgia chapter of the Society of the Cincinnati, and served as a trustee of the Chatham County Academy until his death on December 10, 1789.