Moses Gill was born at Charlestown, Massachusetts, on January 18, 1733, one of the many children of John Gill and Elizabeth Abbot Gill. His family belonged to the industrious commercial and artisan world surrounding Boston. An older brother, John Gill, became the printer and business partner of Benjamin Edes at the Boston Gazette, a newspaper that later played a major role in Patriot politics. Moses followed a different branch of trade, entering business as a merchant rather than the printing shop.

The surviving summaries do not identify a college education or formal apprenticeship for Gill. His early training was probably practical: bookkeeping, weights and measures, correspondence, credit, imported merchandise, and the personal networks on which colonial trade depended. He became a Boston hardware merchant, selling metal goods and tools needed by households, artisans, builders, and ships. The business placed him among both working tradesmen and the merchants who financed Atlantic commerce.

In 1759 Gill married Sarah Prince, daughter of the Reverend Thomas Prince, learned pastor of Boston’s Old South Church. The marriage linked him to a distinguished clerical family and was commemorated by portraits from John Singleton Copley. After Thomas Prince’s death, Moses and Sarah inherited an enormous tract in western Worcester County in the district that became Princeton. The property changed the direction of Gill’s life. He reduced or retired from active Boston business by 1767 and divided his time between the city and a large country estate.

Sarah died without children in 1771. Gill married Rebecca Boylston, member of another influential Massachusetts family, in 1773; that marriage was also childless. He later adopted a nephew. The household’s prosperity included ownership of enslaved people, demonstrating that slavery formed part of elite life even in colonial Massachusetts.

In 1774 he was elected to the provincial assembly.