The Canberra building where John Curtin phoned Winston Churchill to inform him Australia would join Britain in World War II is set to become office space.
In September 2017, the federal government sold the heritage-protected "West Block" building to a subsidiary of the Geocon Land Holding group, a Canberra-based developer, for $6.25 million.
Geocon had planned to turn it into a boutique hotel, but the project did not eventuate.
It has now sold the iconic white and red brick 1928 built property to Oceana Property Partners for more than $20 million.
The sale of West Block, located about 400 metres from Parliament House, was handled by director at Knight Frank, Alex McColl, with the property sourced off market.
"We were pleased to see West Block purchased by a group with such a significant vision for the building, respect for its heritage and its surrounds," Geocon managing director Nick Georgalis said in a statement on Friday.
"West Block is a one off, it is a museum piece in a part of Canberra where development opportunities simply don't present themselves."
