[1] He was the only son of John Parnell (1680–1727), Esq., MP and later Judge of the Court of King's Bench (Ireland), and Mary, sister of the Lord Chief-Justice William Whitshed.
Thomas Parnell was the archdeacon of Clogher in 1705, prebendary of Dublin in 1713, vicar of Finglas in 1718, and poet, friend of Alexander Pope and Jonathan Swift.
He was a Member of Parliament (MP) for Maryborough in 1761, and was created a Baronet of Rathleague, Queen's County, on 3 November 1766.
Sir John married Anne, second daughter of Michael Ward, of Castle Ward, County Down, one of the judges of the court of King's Bench in Ireland and Anna Catherine Hamilton, daughter of James Hamilton of Bangor, County Down.
[4] Sir John Parnell died in 1782, and was succeeded by his only son, Sir John Parnell, 2nd Baronet,[5] knight of the shire for the Queen's County, commissioner of the revenue in Ireland, Chancellor of the Exchequer, Privy Councilor, and Lord of the Treasury[6] He was great-great-grandfather of Irish nationalist leader Charles Stewart Parnell.