Robert Monckton was born on June 24, 1726, the second son of John Monckton, 1st Viscount Galway, and Lady Elizabeth Manners. His family belonged to the British aristocracy and possessed important political connections. As a younger son, Robert was directed toward military service, while his elder brother inherited the family title. He received the education expected of a gentleman officer and entered the army at fifteen, obtaining an ensign’s commission in the 3rd Regiment of Foot Guards in 1741.

Monckton’s first active service came during the War of the Austrian Succession. He campaigned in Flanders and fought at Dettingen in 1743, Fontenoy in 1745, and other actions involving British and allied armies. These battles exposed him to disciplined linear warfare and the problems of maneuvering multinational forces. He rose to captain in the Guards and lieutenant colonel in the army, benefiting from family standing while demonstrating steadiness in service.

In 1752 Monckton received the colonelcy of the 47th Regiment of Foot. The following year he was sent to Nova Scotia and became a member of the colonial council at Halifax. This assignment brought him into a contested borderland inhabited by British settlers, Acadians, Mi’kmaq communities, and French troops. He commanded at Fort Lawrence on the isthmus connecting peninsular Nova Scotia with the mainland and observed the uneasy relationship between imperial officials and an Acadian population that attempted to remain neutral.

By 1754 Monckton had become lieutenant governor of Annapolis Royal. His work combined military command with civil administration, diplomacy, intelligence gathering, and the management of settlements vulnerable to attack. He learned to coordinate regular soldiers with New England provincial troops and to operate in a region of marshes, rivers, small forts, and dispersed communities. This combination of European combat experience and direct familiarity with northeastern North America made him a natural choice for command when Britain moved against the French position at Fort Beauséjour in 1755.