St Mawes Castle is one of a network of coastal artillery forts built along the south coast of England by King Henry VIII to deter French and Spanish invasion. Also known as Henrician castles or device forts, they all share a circular plan that enabled guns to cover every angle. Together with Pendennis Castle on the opposite shoreline, it guarded against the capture of the strategic anchorage at Carrick Roads and the port of Falmouth.

During the English Civil War, as a result of being overlooked by higher ground on the landward side, the Royalist strong hold surrendered to Parliamentary forces without a fight. The castle remained in use for local defence during American Revolution and the Napoleonic wars and into the 20th century. It was finally decommissioned in 1956.