Rev. John Blair was a younger brother of Rev Samuel Blair, and was born in Ulster, Ireland in the year 1720.  He was also an alumnus of the "Log College" at Neshaminy, and a pupil of the elder Wm Tennett.  He was ordained Dec 27, 1742, pastor of 3 churches at Cumberland Co, Pa.  He resigned this charge Dec 28, 1748 and was without a settlement until 1757, when he succeeded his brother Samuel at Fagg's Manor, both as pastor of the church and head of the school.  In this latter capacity he assisted in the preparation of many young men for the ministry.

In 1767 he was chosen Professor of Divinity and Moral Philosophy in the college f NJ, and removed to Princeton.  He was also vice-president of the college and officiated as president until the arrival from Scotland of Dr Witherspoon, who had been elected to the presidency.  He resigned his professorship in 1767 and was pastor of a congregation in Orange Co, NJ.until his death, Dec 8, 1771