During the War of 1812, his policies and victory in the conquest of present-day Maine, renaming it the colony of New Ireland, led to significant prosperity in Nova Scotia.

The end of the American Revolutionary War brought a number of reductions to the army and this included the disbanding of the 85th, and so on 23 June 1785 Sherbrooke transferred to the 33rd Regiment of Foot which was at the time serving in Halifax, Nova Scotia.

[1] After an attempt to join the West Indies Campaign in October 1795 was aborted due to large storms in the English Channel Sherbrooke and the 33rd were instead sent to serve in India, arriving at Calcutta in February 1797.

[1] Sherbrooke was promoted to colonel on 1 January 1798 and as such fought in the Fourth Anglo-Mysore War, participating in the final defeat of Tipu Sultan at the Siege of Seringapatam on 4 May 1799.

[6] The Peace ended in May 1803 with the start of the Napoleonic Wars and Sherbrooke accordingly resumed active service,[7] being given command of the 4th Battalion of the Army of Reserve, a home defence force created to prepare for a French invasion, based at Norman Cross.

[2] While the court of King Ferdinand urged Sherbrooke to make offensive manoeuvres towards mainland Italy with his troops, he instead began to improve Sicily's defences and prepare for a possible French invasion.

[13] Sherbrooke arrived at Halifax on 16 October 1811, as military commander of the Provinces of Nova-Scotia, New-Brunswick, and their Dependencies, including the Islands of Newfoundland, Cape Breton, Prince Edward and Bermuda.

Sherbrooke was able to collect customs dues while he occupied Castine, and these funds were in later years used to finance the Cambridge Military Library in Halifax and to create Dalhousie College.

[2] New Ireland remained under the control of Britain until April 1815, although Sherbrooke himself only stayed there for four weeks, when the Treaty of Ghent restored it to the United States.

[3] While the majority of Sherbrooke's tenure as Lieutenant Governor of Nova Scotia was spent concentrating on the war, he also made a significant effort to increase support for the Church of England, as most of the population were dissenters.

While largescale changes were voted down by the Nova Scotia House of Assembly, he provided small sums of money for the Church via taxation and allotted undeveloped land to it for the construction of religious buildings.

[16] His active defence of the colony during the War of 1812 combined with his proven ability to work competently with the civilian population led to his appointment as Governor General of British North America (fully Captain General and Governor in Chief in and over the Provinces of Lower-Canada, Upper-Canada, Nova Scotia, New-Brunswick, and their several dependencies, Vice-Admiral of the same, Lieutenant-General and Commander of all His Majesty’s Forces in the said Provinces of Lower-Canada & Upper-Canada, Nova-Scotia and New-Brunswick, and their several dependencies, and in the Islands of Newfoundland, Prince Edward, Cape Breton, and Bermuda, &c. &c. &c)[17] in 1816.

[2][16] Sherbrooke continued to work actively into 1817, concentrating on reforming the colony's public finances, but once again was set back by his failing health.

[13] Henry Edward Bunbury said of him that: "the brigade he commanded winced a little under the sharpness of his discipline, while they revenged themselves by comical stories of his rough sayings and impetuous temper...A short, square, hardy little man, with a countenance that told at once the determined fortitude of his nature.

Without genius, without education, hot as pepper, and rough in his language, but with a warm heart and generous feelings; true, straight forward, scorning finesse and craft and meanness, and giving vent to his detestation with boiling eagerness, and in the plainest terms.