He was educated at
Winchester College (1728–1729). 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
frigate Embuscade. 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
Barfleurs
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 Boscawen supposedly 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. ==Succeeds to dukedom==