Background
He was the oldest son of Thomas Southwell, 2nd Baron Southwell and his wife Mary Coke, eldest daughter of Thomas Coke.
He was the oldest son of Thomas Southwell, 2nd Baron Southwell and his wife Mary Coke, eldest daughter of Thomas Coke.
Southwell was educated at Lincoln"s Inn and went then to Christ Church, Oxford.
He served in the 2nd Foot and became an ensign in 1738. Between 1753 and 1757, Southwell was Grandmaster of the Grand Lodge of Ireland. In 1747, Southwell entered the Irish House of Commons for Enniscorthy, sitting for it until 1761.
Three years later, Southwell delivered his maiden speech in the Irish House of Lords.
He was appointed Constable of Limerick Castle in 1750 and Governor of County Limerick in 1762, posts he held until his death in 1780. He was made High Sheriff of County Limerick for 1759.
In 1776, Southwell was elevated to the title Viscount Southwell, of Castle Mattress, in the County of Limerick. Southwell died, aged 59 and was buried at Rathkeale.