The island was first fortified when the British founded Halifax in 1749. During the period of Acadian Deportation 1755 to 1762, the island was sometimes a detention camp for Acadians prior to being shipped to other British colonies. During the 19th century Halifax became a major British naval base and Georges island one of an inter-connected system of harbour defences. As military technology changed, the defences on Georges Island were updated.
The island remained an important seaward defence after the Government of Canada took over the Halifax defences in 1906. Georges Island helped defend the harbour in both World Wars. The island because a national historic site in 1965.