He was educated at Winchester College. He joined the Royal Navy, and on 4 March 1740 was promoted lieutenant aboard. He was promoted captain of on 15 July 1740, and was moved to in July 1741. While commanding Oxford, in 1744 he took part in the Battle of Toulon, and later gave damaging evidence against Richard Lestock. He was moved to in March 1745, and shortly thereafter to. On 11 April 1746 Ruby, with and, was dispatched from Plymouth to join the fleet off Brest, France. Before finding the fleet under Admiral William Martin on 22 May, he was able to capture the French frigateEmbuscade. He was given command of in November 1746 and was sent to the East Indies to serve under Rear-Admiral Thomas Griffin and Admiral Edward Boscawen. He was employed by Boscawen at the Siege of Pondicherry in 1748 to take soundings off Pondicherry, in order to arrange the dispositions of the naval blockade of the town. Upon returning to England in April 1750, Captain Powlett charged Rear-Admiral Griffin with misconduct for failing to engage eight French ships at Cuddalore, a decision which had been generally unpopular among Griffin's captains. Griffin was found guilty of negligence and was temporarily suspended from his rank. Griffin in response court-martialed Powlett on charges including cowardice, which Powlett attempted to escape by going on half-pay. Meanwhile, he entered the House of Commons in 1751 as Member of Parliament for Christchurch. Despite Powlett's evasions, he was court-martialled on 1 September 1752, but was acquitted due to Griffin's charges having failed for lack of evidence. The incident was sensational, and concluded in 1756 with a duel between the two officers on Blackheath. He was appointed to command in January 1753. Powlett's rapid rise to a captaincy and his willingness to commence court martial proceedings against his superiors were a result of his family connections. His father's support of Walpole had made him a Lord of the Admiralty in 1733, a post which he retained until 1742. Even after leaving the Admiralty, the Bolton political connections remained sufficiently strong to ensure his continued promotion. However, he had apparently already become a figure of satire and is believed to have inspired the character of "Captain Whiffle" in Smollett's 1748 novel The Adventures of Roderick Random. In 1754, following his father's succession to the Dukedom, he became known as Lord Harry Powlett, and replaced his elder brother Charles Powlett as MP for the family's pocket borough of Lymington. He was appointed to command on 4 February 1755 and petitioned the Duke of Newcastle, then prime minister, for promotion to flag rank, on the strength of his family's support of the government. However, a damaging accident to his reputation occurred soon after, while acting with Admiral Hawke's fleet off France. Sent on 22 August 1755 to chase a ship to the south-east, he became detached from the fleet. While waiting at the rendezvous on 25 August, the ship's carpenter reported Barfleur's sternpost to be dangerously loose, and Powlett returned to Spithead for repairs. In October 1755 he was court-martialled for having separated from the fleet and returned to port without justification. He was admonished on the first charge and acquitted on the second, and the carpenter was dismissed as incompetent. It was, however, widely believed that the carpenter had served as a scapegoat, and Powlett thereafter was given the sobriquet of "Captain Stern-Post". Notwithstanding this incident, the Bolton influence proved irresistible, and he was promoted rear admiral on 4 June 1756 and Vice-Admiral of the White on 14 February 1758. Feeling ran strongly against him, despite his promotions, and he never again received a naval command, even at the outbreak of the Seven Years' War in 1754. In 1756 supposedly Boscawen requested Powlett's appointment as his second-in-command but was refused by King George II, who shared in the general low opinion of Powlett. In 1761 he again changed constituencies, and was returned as MP for Winchester.
