When Sir George Grey purchased Kawau Island in 1862 he had just returned to New Zealand for his second term as Governor. However it was not until 1870 when he went to live on Kawau with his niece that he began transforming the island into the great estate it later became.

Grey employed Frederick Thatcher to extend the square twenty year old former mine manager's house. Thatcher added a very large new wing with a long verandah and sweeping bay window. The distinctive double verandah arrangement around the large bay at the front of the house was added in 1890.

Inside the house, the large drawing room is filled by Grey's impressive collection of tribal artefacts and heirlooms and part of his priceless collection of rare books later bequeathed to the citizens of Auckland. It was in this room Grey entertained invited guests and excursion parties. Many of New Zealand's most important citizens stayed at the Mansion House which Grey surrounded by extensive gardens of imported trees and plants where an array of exotic animals roamed.

When Grey sold the island in 1888 to retire in Auckland he had turned it into a veritable paradise, with the Mansion House being the central attraction. The house was run as a hotel until 1967 when it was sold to the Government for inclusion in the Hauraki Gulf Maritime Park. The house was reopened in 1979 after extensive renovations.

Finally, as a monument to the vision and zeal of one of New Zealand's most important figures the Kawau Island Mansion House is of the utmost importance.