Soldier and military engineer.
Apprenticed to a wholesale merchant; later studied military engineering under John Henry Bastide, a British army officer who planned fortifications of Boston harbor. Commissioned lieutenant-colonel and captain of artillery train in Louisbourg expedition (1745). Designed several British forts and batteries in New England and Canada. Commander of provincial artillery (1759). Purchased one-half of iron- rich Massapog Pond in Sharon, Massachusetts, from Edmund Quincy (1770); with Quincy, smelted ore and eventually manufactured cannon for the Continental army. Chief engineer of Continental army (1775-76); engineer general of eastern department (1777-80).
Son of Richard and Rebecca Gridley of Boston. Married Hannah Deming (1730); nine children, including Joseph Gridley, who carried ore samples to Franklin (1778). Unitarian.