George Thomas John Nugent, 1st Marquess of Westmeath (17 July 1785 – 5 May 1871), styled Lord Delvin between 1792 and 1814 and known as The Earl of Westmeath between 1814 and 1821, was an Irish peer.
Nugent was born in Clonyn, County Westmeath, the son of George Frederick Nugent, 7th Earl of Westmeath, and Marianne, daughter of Major James St. John Jefferyes. His parents divorced in 1796 after his father's discovery of his mother's affair with Augustus Bradshaw, which also resulted in a celebrated action for criminal conversation.
Lord Westmeath succeeded his father in the earldom in 1821. The following year he was created Marquess of Westmeath in the Peerage of Ireland. As these were Irish peerages they did not entitle him to an automatic seat in the House of Lords. However, in 1831 he was elected an Irish Representative Peer. The same year he was also appointed Lord-Lieutenant of Westmeath, a post he held until his death.
Lord Westmeath was married three times. He married firstly Lady Emily Anne Bennet Elizabeth Cecil, daughter of James Cecil, 1st Marquess of Salisbury, and Lady Emily Mary Hill, on 29 May 1812. They had two children:
Lord Westmeath and Lady Emily divorced in 1827. He married, secondly, Maria Jervis on 18 February 1858. They divorced in 1862. He married, lastly, Elizabeth Charlotte Verner, on 12 July 1864. He had an illegitimate daughter, Eliza Nugent (c. 1806 - 14 September 1877), who married Alfred Harley, 6th Earl of Oxford and Mortimer.
Lord Westmeath died in May 1871, aged 85, when the marquessate became extinct. He was succeeded in his remaining titles by his kinsman, Anthony Nugent. The Marchioness of Westmeath died in September 1882.