Hart’s family were long established in county Donegal, but he was the first to sit in Parliament. His military career involved action in America, the West Indies and the Cape, but principally in India, where he first arrived in 1782, as a.d.c. to Gen. Medows. He was at home from 1783 until 1788, when his wish to return to India was fulfilled. He served as military secretary and adjutant to Medows at Bombay and was deputy paymaster-general of the forces. He subsequently served in the same capacity at Madras, though he fell foul of the supreme council by his insistence on accounting only to the pay office. He served in the campaigns against Tipu Sultan in Mysore. In 1792 Medows summarily replaced him, but he succeeded William Burke as deputy paymaster-general in India until in 1795, ailing—if not ‘in a deplorable state of raving madness’—and still not as prosperous as he wished, he returned home. In 1798 he returned to India and for his services in the final campaign against Tipu accepted £4,000 worth of booty. He failed in a bid to become deputy paymaster to the forces in Ceylon and when he returned home it was in disgrace. He was found guilty by court-martial of peculation in his capacity as commissary of grain to the army of Mysore and suspended. The East India Company dismissed him in 1801, by which time he was serving on the staff in Ireland. He subsequently attempted to clear his name and obtain compensation, but Lord Buckinghamshire, who undertook to secure him £10,000 in 1814, met with his refusal of an inadequate award and the resentment of the court of directors. Nevertheless, he had ‘made money’ in India.
Hart’s brother John was a zealous supporter of Lord Abercorn’s interest in county Donegal. They were related to Henry Vaughan Brooke, one of the sitting Members, who apparently encouraged Hart’s ambition to succeed him. On the death of Brooke late in 1807, Hart unsuccessfully contested Donegal against Lord Conyngham’s nominee, with the support of Abercorn, for which he had angled at the general election, and the approval of administration. He was described as ‘a very wealthy man whose sole ambition is to be in Parliament’. By 1812 the Castle had induced Conyngham to secure his return, the viceroy having no doubt that Hart would be ‘steady with us’.
Hart was a regular attender who could be relied on to support government in general. On Irish questions, the main subject of his occasional speeches, he supported the preservation of the peace bill in July 1814, but he was not uncritical, particularly of the collective penalties imposed by the Illicit Distillation Act, 24 Apr. 1816, which he tried to circumvent in a motion of 30 May 1818 and condemned roundly, 30 Apr., 20 May 1819. He opposed the extension of the property tax to officers employed abroad, 1 May 1815.