Thomas Southwell, 1st Baron Southwell

He was the oldest son of Richard Southwell, son of Sir Thomas Southwell, 1st Baronet, and his wife Lady Elizabeth O'Brien, daughter of Murrough O'Brien, 1st Earl of Inchiquin.[2] His younger brothers were William Southwell and Richard Southwell.[3] In 1681, his father having predeceased him, Southwell succeeded his grandfather as baronet.[4] During the Glorious Revolution of 1689, he and his brother were attainted by the parliament of King James II of England.[5] Southwell was also imprisoned, but was released and pardoned the following year.[5]

In 1695, Southwell entered the Irish House of Commons for Limerick County, representing it until 1713.[6] He was returned for the constituency again from 1715 until August 1717,[6] when he was elevated to the Peerage of Ireland as Baron Southwell, of Castle Mattress, in the County of Limerick.[7] In 1697, Southwell became a Commissioner of the Revenue, however resigned in 1712.[5] He was reappointed two years later and held this post until his death in 1720.[5] In May 1710, Southwell was sworn of the Privy Council of Ireland.[8]

In April 1696, he married Lady Meliora Coningsby, eldest daughter of Thomas Coningsby, 1st Earl Coningsby and his first wife Barbara Gorges.[4] They had six sons and five daughters.[4] Southwell died at Dublin and was buried at Rathkeale.[9] He was succeeded in his titles by his oldest son Thomas.[10] His second son Henry sat also in the Parliament of Ireland.[9]