Grant was called to the bar the same day as his brother, 30 January 1807, and entered into legal practice, becoming King's Sergeant in the Court of the Duchy of Lancaster, and one of the Commissioners in Bankruptcy. He was elected Member of Parliament for the Elgin Burghs in 1818, and for the Inverness Burghs in 1826. The latter constituency he represented for four years. In 1830 and 1831, he was returned for Norwich, and in 1832 for Finsbury. He advocated for the removal of the disabilities of the Jews, and twice carried bills on the subject through the House of Commons. They were, however, rejected in the Upper House, which did not yield on the question until 1858, twenty years after Grant's death. In 1832 he became Judge Advocate General, and in 1834 was appointed Governor of Bombay. As governor, Grant was a law unto himself and under his rule a multitude of large-scale projects were pushed forward which were to transform the shape of British policy in the East. He was a key player in the decision to occupy Aden, which was carried out shortly after his death.