Samuel Smith was born at Carlisle, Pennsylvania, on July 27, 1752, the eldest son of John Smith and Mary Buchanan Smith. His parents belonged to a prosperous Scots-Irish mercantile family. In 1759 the Smiths moved to Baltimore, a rapidly expanding Chesapeake port whose grain trade offered greater commercial opportunity. Samuel was raised with the expectation that he would eventually inherit responsibility for one of the town’s leading merchant houses.

Smith attended a private academy and received the practical and gentlemanly education suited to commerce: reading, writing, arithmetic, bookkeeping, correspondence, geography, and knowledge of trade. His most important training came in the family business. He learned to evaluate cargoes, extend credit, keep accounts, negotiate with ship captains and suppliers, and understand the movement of flour, grain, manufactured goods, and money through Atlantic markets.

As a young man Smith traveled abroad on commercial business, gaining direct knowledge of European trade and the risks of shipping. His father’s position gave him connections, but the demands placed upon an eldest son also required reliability and disciplined judgment. He returned to Baltimore prepared to take an increasing role in the firm. The city’s merchants were becoming politically influential as British taxation and commercial regulation provoked colonial resistance.

Smith entered military affairs before independence. He joined Baltimore’s militia and acquired the organizational skills expected of an officer: recruiting, drill, supply, correspondence, and command. In 1776 Maryland’s revolutionary authorities reportedly sent him to Annapolis in connection with the removal of royal governor Robert Eden and the seizure of official papers. Later that year he received a Continental commission.

He served as captain, major, and lieutenant colonel in the Continental Army. He took command at Fort Mifflin in 1777.