In 1775, before the American War of Independence broke out, he led troops to Salem, Massachusetts looking for contraband weapons. His advance was delayed by a standoff at a bridge, during which the colonists removed the weapons he was looking for. His force was eventually allowed to proceed, but found nothing of consequence, and was received with hostility during the expedition.
In 1780, he was sent to the Chesapeake Bay by Sir Henry Clinton in order to "make a powerful diversion in [Earl Cornwallis's] favor by striking at the magazines then collecting by the enemy ... for supplying the army they were assembling to oppose him."[4] He became major general in 1782 and was made Colonel of the 63rd (West Suffolk) Regiment of Foot the same year. He transferred in 1788 to be Colonel of the 9th (East Norfolk) Regiment of Foot to his death.
Personal life
In 1760, he married Mary Tullidelph, a daughter of Dr. Walter Tullidelph of Tullidelph, in the County of Forfar, who had been a planter and member of the Council of the Island of Antigua. She died in 1761 in childbirth. Their daughter survived:[5]
On 27 December 1794, on his way back to Edinburgh, Leslie was seized with a dangerous illness, and died at Beechwood House, about three miles west of Edinburgh, on 27 December 1794.[4]