Educated at Wimborne Grammar School and the Royal Military Academy, Woolwich, Hewett was commissioned into the 70th Regiment of Foot in 1762.
[1] In 1771, he went to New York to help control the Carib Uprising and in 1780 he took part in the Siege of Charlestown.
[1] In 1787, he was appointed Commanding Officer of the 43rd Regiment of Foot and in 1791, he went to Ireland where he became Adjutant-General (serving there until 1799).
[1][3] He returned to England, where he served as Inspector General of Recruiting for the British Army from 1798 to 1804.
[1] He was created a Baronet, of Nether Seale in the County of Leicester, on 6 November 1813.