Tutor at the College of New Jersey (Princeton) (1754-56). Licensed as a Presbyterian preacher (1756). Pastor of churches at Big Spring (1757-69), Carlisle (1759-72), and Monaghan, and of the Third Presbyterian Church of Philadelphia (1772-90). Chaplain of Continental Congress in conjunction with Rev. William White. Pennsylvania militia captain. Member of the American Philosophical Society (1779). Popular evangelical preacher.
Son of George and Margaret Duffield of Lancaster County, Pennsylvania. Educated at the College of New Jersey (B.A. 1752). Married (1) Elizabeth Blair (1756). Married (2) Margaret Armstrong, sister of Gen. John Armstrong (1759).
First letter in correspondence: May 1, 1788; DAB; Early Proceedings of the American Philosophical Society . . . from 1744 to 1838 (Philadelphia, 1884), p. 102.