Finance minister Mathias Cormann on Tuesday confirmed East Block, home to the National Archives of Australia, and West Block would be sold off as early as mid-2017.

It will be the first time land has been up for sale within the Parliamentary Triangle, which takes in some of Australia's most prominent buildings including Parliament House, Old Parliament House, the High Court and the National Gallery of Australia.

The announcement comes months after the sale was flagged of two other ageing Commonwealth office blocks, Anzac Park East and West.

However the buyers of those sites will have to knock them down and rebuild as a condition of purchase.

It is understood East and West Block will be protected from demolition through provisions in the Crown lease and sale documentation to preserve the heritage values of both buildings.

But because of changes to the National Capital plan, the sites can be as private sector offices, hotel accommodation or serviced apartments. The buildings will not be able to be used for residential purposes.

"Private investment will support urban renewal, revitalisation of heritage buildings, reopening of the former restaurant building next to Anzac Park West and the overdue rebuild of Anzac Park East, which has been unusable for decades," Senator Cormann said in a statement.

The federal government will call for expressions of interest for West Block and Anzac Park East and West after pre-sale preparation is finalised.

East and West Block were designed by Old Parliament House architect John Smith Murdoch.

Built in 1925-6, East Block has been home to the National Archives head office since 1998 but was once the General Canberra Post Office and the point from which all distances in Canberra were measured.

West Block was opened for government use in 1927 and was once home to the National Library, the Crown Solicitor's office and the Australian Electoral Commission. It is currently vacant.

The building also includes a World War II bomb shelter, which was used during the war to code and decode messages between Australian Prime Minister John Curtin and British Prime Minister Winston Churchill.

Walter Burley Griffin Society Canberra chapter convener Brett Odgers expressed dismay that the buildings would soon be out of public hands.

"The Parliamentary Triangle is highly symbolic, it is a diagram of our federation and our democracy, our system of government and the checks and balances in the system from the High Court through to the people's assembly to the government departments and the executive themselves," Mr Odgers said.

"With the privatisation of government offices in Barton it's quite clear that the losers here have been the taxpayers of Australia and the ratepayers of the ACT because of the inevitable higher costs, higher rents that flow from selling off government assets to the private sector.

"That money could be better spent on national capital initiatives, memorials, monuments and the main cultural institutions which are so strained for finances these days."

The sale of the buildings has been on the cards since 2015, when the Abbott government commissioned a scoping study for selling the John Gorton and Treasury buildings, East and West Block and Anzac Park East and West on the basis they were ageing and expensive to maintain.

It is understood that future tenancy arrangements for National Archives are being finalised now as part of East Block's preparation for sale.

A National Archives spokeswoman confirmed their headquarters was not being moved to their new purpose-built facility in Mitchell, where a quarter of their collection will reside from July.

ACT Property Council chief executive Adina Cirson said the sale would generate a great deal of interest from the property sector but would have to come with caveats.

"There's no point in us having empty office blocks sitting in those key locations so there will come time in the city's development that we have to renew and revitalise those areas just as we are doing right across the city but certainly [we need to be] maintaining the sophistication that our capital deserves in that area," Ms Cirson said.