Thomas Southwell, 1st Baron Southwell

In 1695, Southwell entered the Irish House of Commons for County Limerick, 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 also sat in the Parliament of Ireland.^[9]