Colonel Thomas Pride, the instigator of Prides Purge the only military coup dtat in English history was stationed on the island in 1654. 11 Sir Robert Clayton, a Lord Mayor of the City of London and wealthy merchant became owner in the mid-1650s and after his death in 1707 the island was sold to William Benson, a Whig Member of Parliament and architect.

The island is owned by the National Trust with the northern half managed by the Dorset Wildlife Trust.

Much of the island is open to the public and includes areas of woodland and heath with a wide variety of wildlife, together with cliff top views across Poole Harbour and the Isle of Purbeck.

Access is by public ferry or private boat; in 2017 the island received 133,340 visitors.

The islands name probably comes from Anglo-Saxon Brnoces eg Brnocs island.

The island can be reached by one of the public ferries or by private boat.

The island is 1 1 2 miles (2.4 km) long and 3 4 mile (1.2 km) wide and consists of 500 acres (200 ha) of woodland (pine and oak), heathland and salt-marsh.

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.

Until 31 January 2020, it was also within the South West England constituency of the European Parliament.

Ecological succession has taken place on the island to create topsoil able to support ecosystems.

This reserve includes a brackish lagoon and area of woodland.

Other ecosystems on the island include salt marsh, reedbed, two freshwater lakes, alder carr, coniferous woodland, deciduous woodland and arboretum.

In the past invasive species such as rhododendrons, also non-native, were introduced to the island, but the trusts have cleared many areas.

The entire island is designated a Site of Special Scientific Interest.

The Brownsea red squirrel population is the only population known in the UK to carry the human form of the bacteria stem Mycobacterium leprae that causes leprosy in humans.

Brownsea also has a small ornamental population of peacocks.

In the past the numbers have been higher than the island can sustain and have overgrazed.

To try to limit damage to trees and other vegetation by deer, areas of the island have been fenced off to provide areas of undamaged woodland to allow other species such as red squirrels to thrive.

The chapel was dedicated to St Andrew and the only resident of the island was a hermit, who may have administered to the spiritual welfare of sailors passing through Poole Harbour.

Henry VIII recognised the islands strategic importance of guarding the narrow entrance to the expanding port of Poole.

As part of a deterrent to invasion forces from Europe, the island was fortified in 1547 by means of a blockhouse, which became known as Brownsea Castle.

In the following centuries, the island passed into the hands of a succession of various owners.

In 1576, Queen Elizabeth I made a gift of Brownsea to one of her court favourites and rumoured lover, Sir Christopher Hatton.

During the English Civil War, Poole sided with Parliament and garrisoned Brownsea Castle.

Colonel Thomas Pride, the instigator of Prides Purge the only military coup dtat in English history was stationed on the island in 1654.

Sir Robert Clayton, a Lord Mayor of the City of London and wealthy merchant became owner in the mid-1650s and after his death in 1707 the island was sold to William Benson, a Whig Member of Parliament and architect.