John Marsh was born on November 2, 1742 in Haverhill, Massachusetts. He graduated from Harvard in 1761 and in 1765 he received his license to preach. Between 1771 and 1773, Marsh was employed as a tutor at Harvard. On January 12, 1774 John Marsh was ordained as the minister of the First Church of Christ in Wethersfield, Connecticut, a position he held for 48 years until his death. He married Ann Grant of East Windsor, Connecticut in December of 1775. They had seven children together, three boys and four girls, though the youngest son died very young.

John Marsh was a life-long academic and proponent of education. In 1801, he was elected Fellow of Yale College and retained the position for 19 years. In either 1806 or 1808, John Marsh received his Doctor of Divinity from Yale. As a pastor, he provided monetary assistance for some young men to continue their education. His eldest and middle sons too pursued academic careers. The eldest son, Ebenezer Grant Marsh, was employed as a professor-elect of languages and ecclesiastical studies at Yale before his death in 1803. The middle son, John Marsh Jr. (April 2, 1788 – August 4, 1868), graduated from Yale in 1804, became a minister and advocate for the temperance movement, and received his Doctor of Divinity in 1852. John Marsh was also described as a patriotic supporter of independence from Britain and the continental army.

John Marsh died on September 13, 1821 following a short illness. He was survived by his wife, four daughters, and John Marsh Jr.