Charter Hall's Prime Office Fund has acquired the five-storey office proposed for 15 Sydney Avenue, Barton from Doma and Kenyon Investments.

As part of the deal, the fund will provide finance for the design and construction costs. It will then take ownership and become the ATO's landlord upon completion.

Doma lodged a works approval application with the National Capital Authority last week with the intention to start construction in April 2023.

Last week The Canberra Times exclusively revealed the ATO had signed a 15-year lease for the new building, at a cost of $323.4 million.

ATO staff will pack up their Civic offices and make the move over the lake in 2025.

According to industry sources, Charter Hall is also undertaking due diligence on the current ATO office in Civic for a purchase price of about $300 million.

Charter Hall group managing director and group CEO David Harrison said Canberra's low vacancy rate was an appealing factor.

"We are delighted to extend our partnership with both DOMA and the Commonwealth government as a long-term tenant customer, as we modernise our office portfolios and select low vacancy markets which will drive long-term growth for our investors," he said.

Doma and Kenyon Investments teamed up to acquire the 11,560-square-metre Barton site, known as block 3 section 22, from the Department of Finance in 2019.

They reportedly paid $38 million for the site.

Once complete, the building will provide over 33,000 square metres of net lettable area and will boast strong sustainability credentials.

The developer will target a 4.5-star NABERS energy and five-star Green Star ratings for the new building.

Charter Hall office CEO Carmel Hourigan said the acquisition is in line with the fund's strategy to invest in sustainable and well-positioned buildings.

"This additional brand-new office project will extend our office [funds under management] to $29 billion including committed developments, and reduce the weighted average age of our office portfolio towards eight years," she said.

Doma will engage Canberra builder Bloc to deliver the project.

"This will be our sixth Commonwealth pre-committed office and our third office for the ATO following the ATO Albury and ATO Gosford projects," Doma general manager development Gavin Edgar said.

Charter Hall has become a prominent name in Canberra's commercial real estate market as the property investment and funds management firm continues its buying spree in the capital.

In 2021, Charter Hall teamed up with Singapore-based GIC to purchase 50 Marcus Clarke Street for $335 million.

The building is wholly tenanted by the federal government's Department of Education, Skills and Employment.

Before the year's end, Charter Hall purchased the ActewAGL office building at 40 Bunda Street for $76 million and 24 Wormald Street, Symonston, leased to the Attorney-General's Department, for $36 million.

Charter Hall currently owns the Louisa Lawson Building in Tuggeranong, 44 Sydney Avenue in Forrest and the Telstra head office building in Civic.

The group is also set to acquire the Geoscience building in Symonston for more than $370 million, which would set a new commercial property record for the ACT.

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