John was the son of Henry Hatsell (1701-1762) a bencher of the Middle Temple; and grandson of Sir Henry Hatsell, SL Baron of the Exchequer (1641-1714).
He was educated at Queens' College, Cambridge, where he matriculated in 1751, graduated B.A. in 1755 and M.A. in 1760. He studied law in the Middle Temple, of which society he became senior bencher. He was clerk assistant in the House of Commons at the close of the reign of George II, and became chief clerk in 1768.
He was the author of:
- ‘A Collection of Cases of Privilege of Parliament, from the earliest records to 1628,’ London, 1776. In the British Museum there is a copy with copious manuscript notes by Francis Hargrave.
- ‘Precedents of Proceedings in the House of Commons, under separate titles; with observations,’ 4 vols. London, 1781; second edit. 1785–96; third edit. 1796; fourth edition with additions by Charles Abbot, 1st Baron Colchester, 1818. Colchester knew him well, and acknowledged him as the best authority on parliamentary procedure.