Brownsea Island by third parties, is owned by the National Trust. Most of the buildings are situated near the small landing stage. The northern portion of the island is a Nature Reserve managed by Dorset Wildlife Trust and an important habitat for birds; this part of the island has limited public access. A small portion to the southeast of the island, along with Brownsea Castle, is leased to the John Lewis Partnership for use as a holiday hotel for staff, and is not open to the public. The island forms part of the Studland civil parish in the Purbeck local government district.
Brownsea Island Viking raid to the harbour and used Brownsea as a base to sack Wareham and Cerne Abbey. In the 11th century the owner of the island was Bruno, who was Lord of the Manor of Studland. Following his invasion of England, William the Conqueror gave Studland, which included Brownsea, to his half-brother, Robert de Mortain. In 1154, King Henry II granted the Abbot of Cerne the right of wreck for the island and the abbey continued to control the interests of Brownsea for the following 350 years. After the Dissolution of the Monasteries, control of Brownsea passed to the Crown.