Property magnate Mr Gandel, who regularly ranks in the top 10 of the BRW Rich 200 list, and his wife were founding donors in 1982 and have been close to the gallery ever since.

Mr Gandel said the gallery had an essential role in developing the national art collection for future generations of Australians.

''Pauline and I hope that our support will inspire others to follow in our footsteps,'' he said.

Director Ron Radford said roughly half the money would be used for the construction of the new great hall, part of the gallery's current redevelopment, and the rest for acquisitions for the national collection.

''This wonderful act of generosity by Mr and Mrs Gandel will be honoured by the National Gallery of Australia through the naming in perpetuity of the new function hall which will be known as the Gandel Hall,'' Mr Radford said. ''This is an historic time for the National Gallery and the support from Pauline and John Gandel will help us to continue to develop the national art collection and to make the gallery experience more accessible and exciting.''

Mr Radford said he could not give a date when the new Stage 1 redevelopment would be opened because it depended on the outcome of last Saturday's federal election (Australia's prime minister had been due to open the new section in early September).

For more on this story, including details of what visitors will find in the new sections of the gallery, see the print edition of today's Canberra Times.