East and West Block were put up for sale earlier in the year, part of a federal government fire sale on its ageing office space.

But the High Court ruled a senior cabinet minister key to the sale ineligible to sit in parliament, under section 44 of the Constitution.

As federal local government and territories minister, Nationals deputy leader Fiona Nash revoked the designation for the Commonwealth office blocks, clearing the way for their sale.

Her decision about East Block came after she told the Senate she may be a British citizen.

The High Court last month ruled Ms Nash - along with former deputy prime minister Barnaby Joyce, former Greens senators Scott Ludlam and Larissa Waters and One Nation's Malcolm Roberts - was ineligible to sit in parliament.

Canberra development company Geocon bought West Block for $6.25 million in September with plans to turn it into a luxury hotel, while East Block - home to the National Archives - is still up for sale.

But Greens MLA Caroline Le Couteur said the High Court ruling gave the federal government an opportunity to reconsider selling the buildings.

"Canberra's purpose is to be the national capital. The Parliamentary Triangle is the heart of the national capital, it's got new Parliament house, it's got Old Parliament House. East and East Block were built to be the administrative centre of Australia and it's really important that we keep our heritage. This is literally why Canberra is here," Ms Le Couteur said.

"We haven't sold off any parts of the Parliamentary Triangle before, it's a very poor precedent and we'd like to see it changed."

Constitutional law expert George Williams said the Greens did have a case.

"Such decisions now lack clear legal support. It is quite possible though that the high court will uphold such decisions on pragmatic grounds," Professor Williams said.

However finance minister Mathias Cormann said the government remained "committed" to the sale of the buildings.

"These buildings are surplus to the Government's requirements and attracting private investment through the sale of those buildings provides a great opportunity to revitalise these properties and to ensure their significant heritage values are retained," he said.

Geocon's managing director Nick Georgalis said he was "not at all" concerned that the sale could be overturned.

"Geocon looks forward to creating a new hotel that will celebrate the heritage aspects of the West Block buildings, inside and out, and, for the first time, open up these historic structures to the public," Mr Georgalis said.

"We will be breathing life into the precinct through the preservation and reinvigoration of an important heritage site."