Thomas Beaumont was born on 29 April 1758, only son of Thomas Beaumont of The Oaks, Darton, Yorkshire and Anne, daughter and co-heiress of Edward Ascough of Louth, Lincolnshire. Educated at University College, Oxford he in 1786 married Diana, natural daughter and eventual heiress of Sir Thomas Wentworth Blackett, 5th Bt. Thomas Beaumont had inherited a relatively modest estate in Yorkshire and initially made the army his career until his regiment, the 22nd Dragoons, was disbanded in 1783; thereafter he served with the 21st Dragoons eventually attaining the rank of colonel. He disappears from the Army Lists after 1802. Upon the death of his wife's father in 1792 he found himself scion of her vast estates of Bretton Hall, Yorkshire and Hexham Abbey, Northumberland, together with lead mines and other concerns bringing in in excess of £100,000 per annum. Elected M.P. for Northumberland in an unopposed by-election in 1795, he served until 1818, speaking little but known both for his support of the abolition of the slave trade and his vote against Catholic relief.
With their family of five sons and three daughters the Beaumonts traveled between their homes, entertaining on a lavish scale as the social diarist Mary Russell Mitford comments: 'They live in immense style at the Abbey; thirty of forty persons frequently dine there; no servants but their own admitted; and there is constantly a footman behind every chair.... he lives in the most princely magnificence'. His character is thought to have been formed by that of his formidable wife, as Miss Mitford notes: 'Colonel Beaumont is generally supposed to be extremely weak.... but I sat next to him at dinner, and he conducted himself with infinite propriety and great attention and politeness; yet, when away from Mrs Beaumont, he is (they say) quite foolish; and owes everything to her influence with him.' Although he applied several times for peerages the applications were unsuccessful. He died in July 1829 and was succeeded by his son Thomas Wentworth Beaumont.