The Australian Taxation Office headquarters at 21 Genge Street in Civic is expected to fetch a sale price in the high-$300 million range.

Spanning a 5776-square-metre block between Bunda and Cooyong Streets, the 10-storey building was developed by QIC in 2007 and was later sold to German-based investment fund Real I.S. Australia.

CoreLogic records show the property changed hands in 2009 for $204.5 million.

The investment fund also owns the Geoscience building in Symonston, which was listed for sale in February.

The Genge Street asset includes more than 43,000 square metres of net lettable area with an estimated $22.2 million net passing income.

The ATO's 15-year lease, valued at more than $310 million, was set to expire in November this year but has been extended until November 2027.

Commercial property agencies Knight Frank and Cushman and Wakefield are leading the expressions of interest sale campaign.

Sean North, head of Canberra at Knight Frank Australia, said he expects interest from local institutional investors and international parties.

"We do have a group over in Singapore at the moment talking to a number of sources of capital," he said.

"We expect there to be quite a bit of interest in the asset. It's a large-format, great location to the CBD - this type of opportunity doesn't typically come up very often."

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With its current price expectations, the property stands to break the commercial sales record for Canberra, set last year when 50 Marcus Clarke Street sold for $335 million.

The Geoscience building is also a frontrunner for a record-breaking sale, tipped to fetch more than $360 million.

Mr North said 21 Genge Street would certainly sell for beyond Canberra's $335 million record.

"How much higher will be determined by the market, of course, but ... it'll certainly be up there," he said.

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