John was born on 12 May 1730, the son of Dr. Richard Warren and Priscilla Fenner, at Cavendish, Suffolk, where his father was the rector.|
He was educated for seven years at Bury St. Edmunds school, and was admitted a sizar of Gonville and Caius College, Cambridge, on 6 July 1747.
On this foundation he was a scholar from 1747 to 1754, and from it he graduated B.A. as seventh wrangler in 1750, taking his M.A. degree in 1754, and gaining the Member's prize in 1753.
He was ordained deacon on 17 June 1753, and took priest's orders on 26 May 1754.
He was then presented to the rectory of Leverington in the Isle of Ely, and became chaplain to Edmund Keene bishop of Ely, who collated him to the rectory of Teversham in Cambridgeshire.
He was appointed the seventh prebend of Ely on 23 January 1768, and the same day, on his resigning Teversham, he was appointed to the rectory of Snailwell in Cambridgeshire.
He acted for some time as chaplain to Lord Sondes, and as chaplain and secretary to Matthias Mawson, bishop of Ely.
In 1772 he proceeded to the degree of D.D. in the university of Cambridge,
He was nominated to the bishopric of St. David's on 3 August 1779, on the translation of James Yorke to Gloucester, and on 15 May 1783 he was elected to the see of Bangor on the advancement of John Moore (1730-1805) to be archbishop of Canterbury.
He died on 27 January 1800 at his house in George Street, Westminster, and was buried on 10 February in the north aisle of Westminster Abbey.
He married on 12 April 1777, Elizabeth, daughter of Henry Southwell of Wisbeach, Cambridgeshire, who brought him a considerable fortune.
Warren was a prelate of the greatest application to business, undoubted talents, candour, and integrity.
No man was more accurate, and it was in all probability for these reasons, and from the high position his brother occupied in the medical profession, that he was chosen chairman of the committee when the House of Lords threw out the bill of the Surgeons' Company in 1797.
There is a portrait of Warren in the hall of Caius College.