Thomas Anthony Southwell, 3rd Viscount Southwell KP (25 February 1777 – 29 February 1860) was an Irish peer. He became Viscount Southwell in 1796 on the death of Thomas Southwell, 2nd Viscount Southwell and was appointed a Knight of the Order of St Patrick on 12 September 1837. He was lord of the manor of Garway at Garway House in Herefordshire.