Pendennis Castle was built by Henry VIII in 1540-45 as one of a pair of artillery forts to protect this strategic area from the threat of invasion from Catholic France and Spain. St Mawes Castle was built on the opposite headland and between them their cannon could cover the entire entrance to the Fal estuary.

The land on Pendennis Head was leased from a prominent local family, the Killigrews, who provided several Captains of the castle. In the mid 17th century Sir Peter kiligrew was given the grant for a new town, Falmouth, which grew in the shadow of Pendennis Castle. Unlike St Mawes Castle which has remained largely unchanged since its construction, Pendennis has experienced many improvements and changes since the original castle was built. At its centre is the Henrician castle consisting of a round gun tower encircled by a low gun platform, and a projecting entrance block. In 1588 ramparts and angle bastions were erected to protect the high ground of the peninsular. These were further developed in the earl 17th century and put to the test during a six month siege of the castle in 1646, during the Civil War, when the castle was defended for the Royalist cause. A lack of food finally forced the garrison to surrender to the Parliamentary army of Sir Thomas Fairfax.

The castle continued to develop with various buildings, storehouses and barracks constructed and later demolished or replaced, and its weapons updated to counter the threat of invasion through to its final active service during the Second World War. Reconstructions in several rooms allow visitors to experience life in the castle during different periods.