This distinguished officer entered the service in 1759 as a cadet in the Royal Artillery, and was appointed ensign in the fifth fusiliers on the 30th of July, 1762; he was promoted to be lieutenant on the 2nd of July, 1765, was appointed adjutant in 1767, and promoted to the rank of captain on the 25th of July, 1771. In May, 1774, Captain Harris embarked for America, and was present in the first action of the American war, namely, at Lexington, on the 19th of April, 1775. At the battle of Bunker’s Hill on the 17th of June following, he was severely wounded in the head, and obliged to be trepanned, which caused him to be sent to England; but he returned in time to take the field previously to the landing of the British army on Long Island in August, 1776. Captain Harris was present at the affair of Flat Bush; in the skirmishes on York Island; in the engagement at White Plains; at Iron Hill (where he was shot through the leg), and in every action up to the 3rd of November, 1778, except that of Germantown. In 1778 he was promoted to the rank of major in the fifth fusiliers, and embarked with the regiment for the West Indies with the force under Major-General James Grant, by whom he was appointed to command the battalion of grenadiers, and landed with the reserve of the army under Brigadier-General Medows, at St. Lucia on the 25th of December. After the taking of Morne Fortunée, Major Harris was second in command under Brigadier-General Medows at the post of La Vigie, where the French were repulsed in their repeated attacks, and in consequence they retreated from the Island. Immediately after the departure of the French armament, the Governor surrendered the Island of St. Lucia to the British troops, the capitulation being signed on the 30th of December, 1778. In 1779, Major Harris embarked with the fifth fusiliers, which were ordered to serve as marines, and was present in the engagement off Grenada, under Admiral Byron, on the 6th of July, 1779. In 1780, Major Harris returned to England, and in December of that year succeeded to a lieut.-colonelcy in the fifth fusiliers, from which he exchanged into the seventy-sixth regiment, and accompanied to the East Indies, as secretary, Sir William Medows, who was appointed Governor and Commander-in-Chief of Madras. Lieut.-Colonel Harris served in the campaigns of 1790 and 1791 against Tippoo Sultan; in the action of the 15th of May, 1791, he was appointed by General the Earl Cornwallis to command the second line; he was also personally engaged in the attack of the Sultan’s camp and of the Island of Seringapatam, on the night of the 6th of February, 1792, the success of which terminated that war. Peace being re-established, Lieut.-Colonel Harris returned with Lieut.-General Sir William Medows to England. On the 18th of November, 1792, he was promoted colonel by brevet, and on the 3rd of October, 1794, he was advanced to the rank of major-general,