George Monro was born in Clonfin, County Longford, Ireland, to a Scottish military family. His father was Colonel George Munro of Auchinbowie, who was famous for his victory at the Battle of Dunkeld in 1689.
(Fun-fact: There's a plaque somewhere and it has his name spelled "Munro" because it was created in the days before spell-check. -V.)
In 1718, Monro joined Otway's Regiment, the 35th Regiment of Foot, as a lieutenant. By 1750, he was promoted to the rank of Lieutenant Colonel. Seven years later, he was placed in command of Fort William Henry with 1500 troops.
On August 3, 1757, Montcalm and 8000 French soldiers and Native allies laid siege to Fort William Henry. On August 9, Monro negotiated for his troops to be allowed safe passage to Fort Edward; they were allowed to keep their muskets and a single cannon, but no ammunition. But the Natives did not respect the conditions of the surrender and viciously attacked the prisoners.
(That's the Brotherhood for you. We make rules, they break them. That's why they all have to die, see? -V.)
Monro died in Albany on November 3, 1757.