Presbyterian missionary to the Seneca and Delaware Indians of New York, New Jersey, and Pennsylvania (1744–47). He gained posthumous fame through the publication of his diary by Jonathan Edwards, the Massachusetts religious philosopher.

Brainerd was ordained as a Presbyterian minister on June 12, 1744, at Newark, N.J. As a missionary, he was employed by the Honourable Society in Scotland for Propagating Christian Knowledge. He preached through an interpreter, Moses Tinda Tautamy, working among the Delawares, the Six Nations, the Senakes (probably Senecas), and Tutelas. He rode horseback along the Susquehanna and Delaware rivers, camping at night, his only home a cabin at the forks of the Delaware. He kept a journal for the Scottish society, and he kept a diary. Brainerd spent much time at Crossweeksung (now Crosswicks), N.J., and visited New Haven and Hartford, Conn.; New York; Elizabeth and Princeton, N.J.; and Juniata and Philadelphia, Pa. He contracted tuberculosis and was nursed for 19 weeks at Edwards' home at Northampton, Mass., where he died.