George Johnstone was appointed
ensign in the
29th Regiment of Foot on 1 November 1780. He was promoted to
lieutenant in 1787,
captain lieutenant in 1792,
adjutant in 1793 and
captain in 1794. During this time, the regiment was based at various locations in England, but in early 1793, they were posted to
Hilsea Barracks near
Portsmouth, where they were to provide detachments of soldiers to act as
marines aboard
Royal Navy warships during the
War of the First Coalition. At the end of December 1794, Johnstone joined a battalion of 21 officers and 640 men, formed from those in the 29th who were not detached to warships; they embarked on the
troopship Maria for the
Caribbean island of Grenada, where discontent would lead to an insurrection, known as Fédon's Rebellion or the Brigand's War, in the coming months. On their return to England in July 1796, the battalion had been reduced by battle casualties and disease to 5 officers and 87 men. Johnstone was promoted to
major in 1799. The British province of
New Brunswick was regarded as strategically important because of its border with the United States; however, the appointed
lieutenant governor,
Thomas Carleton, had returned to the United Kingdom early in 1803 and refused to return in a dispute about seniority. Therefore, the duties of the office fell upon the senior British officer in the province, a role undertaken by Johnstone between December 1808 and April 1809. Johnstone wrote to the
Governor General, Sir
James Henry Craig, requesting a temporary promotion to
brigadier general so that he could wield more influence with the
Legislative Assembly and asking for compensation for his loss of pay caused by relinquishing command of his regiment while in office; however, neither request was accepted before the end of his tenure. After resuming command of the New Brunswick Fencibles, Johnstone returned to the United Kingdom on leave in December 1809. While at home, he was posted to command the
93rd (Highland) Regiment of Foot, which had been on garrison duty in the Cape Colony (in present-day
South Africa) since their participation in the
Battle of Blaauwberg in 1806. He remained with the regiment there for four years until he was summoned home and promoted in 1814. == Waterloo campaign ==