James Mercer was born on February 26, 1738, at Marlborough in Stafford County, Virginia. He was the son of John Mercer, a prominent lawyer, author, and landowner, and Catherine Mason Mercer. His younger brother George Mercer later became a soldier and colonial official. The Mercer household combined plantation privilege with exceptional legal learning. John Mercer assembled a major library and produced an influential digest of Virginia law, so James grew up where books, court business, land claims, and political discussion were part of family life. The estate’s prosperity also depended upon enslaved labor, a central fact of the Chesapeake society that educated and enriched the Mercers. James received the private instruction customary for a wealthy planter’s son. His father’s legal expertise offered an unusually direct professional education, and James read law under paternal supervision rather than following a modern law-school curriculum. This apprenticeship involved studying English statutes and cases, copying documents, observing litigation, and learning the complicated mixture of English precedent and colonial enactment used in Virginia courts. Family connections widened his horizons. The Mercers were related to the Mason family and interacted with many of the colony’s leading lawyers and officeholders. At the same time, James witnessed the difficulties produced by land speculation, contested western claims, and the management of large estates. Those experiences prepared him for a career in which property law and public policy frequently overlapped. After qualifying for practice, Mercer began building a reputation at the Virginia bar. He married Eleanor Dick, establishing his own household, though she died young; he later married a second time. Before revolutionary politics brought him wider notice, he had already become a working attorney and local gentleman shaped by his father’s formidable example.