He studied law in Edinburgh and Leipzig before joining the British Army at the age of 22. In 1762, then captain, he went with his regiment to Ireland, where he was stationed for ten years or more, and had the opportunity to study the country, which he found very useful many years later.
As MP for Clackmannan (1774-1780) he used to vote according to his principles rather than his patrons, and as a soldier he refused to serve against the American colonists; he was promoted to major general (1787) and made a Knight of the Kingdom for his service in the Netherlands.
After campaigning in the West Indies (1795–6), where he showed clear concern for the welfare of his men, he was appointed commander-in-chief of government forces in Ireland. While touring the country, he formed a low opinion of the upper class and opposed his efforts to use the army as a local police force, stationing small detachments on or near his properties. It attempted, with limited success, to discipline and contain the army and concentrate it into units of reasonable size to make it a respected and effective fighting force. On February 26, 1798, he issued a famous order lamenting the “irregularities” and describing the army as “in a state of debauchery that must make him formidable to all but the enemy“The order drew criticism from other officers and created a political furor. Speaker John Foster led a clique against him. AbercrombyAlthough generally supported by Lord Lieutenant Camden, he disagreed with him on the power of the military to act without civil authority. He resigned his command in mid-March and left Ireland in late April, less than a month before open rebellion began, without having achieved reforms that would have made the military forces more effective.
After serving as head of garrisons in Scotland for eighteen months, Abercromby he commanded a division in the Netherlands, and rejected a title of nobility for his services. While commanding British troops in the Mediterranean, he defeated the French at Aboukir (Abu Qir), near Alexandria (March 21, 1801), but was mortally wounded; He died on March 28, 1801, and was buried in Malta. Monuments were erected in his honor in Malta, at St. Paul’s Cathedral, London, and at St. Giles, Edinburgh. He married Mary Anne Menzies (died 1821) on November 17, 1767, in Ferntower, Perthshire; they had seven children. His widow was named a baroness (1801).