The now-defunct agency's former chief executive, David Dawes, and deputy chief executive, Dan Stewart, appeared on Wednesday before an ACT Assembly inquiry probing the purchase of nine parcels of land between 2014 and 2017.

The agency's former financial bosses also fronted the committee, revealing they had no oversight and were never directly consulted on the multi-million dollar land acquisitions.

The deals to purchase 3,378 hectares of rural land were the subject of a scathing 2018 auditor-general's report, which found they lacked probity.

But in evidence spanning more than an hour, Mr Dawes defended his former agency's conduct, while offering fresh insight into why it proceeded with buying large swathes of rural land - despite the ACT government's pivot to urban infill.

Mr Dawes and Mr Stewart said one of the triggers for buy up was an agency "planning day" in early 2014, during which board members raised concerns about the government's future land supply.

Mr Stewart subsequently prepared a more detailed report for the board, which predicted the government would run out of land to sell by 2031.

The agency's board was "sufficiently concerned" - even "alarmed" - by the report's findings that it was escalated to cabinet, Mr Stewart said.

Mr Dawes said the report was "not adopted" by cabinet, although he rebuffed suggestions that the government did not "agree" with its contents.

Liberal committee member Vicki Dunne pressed Mr Dawes on whether the report made specific recommendations about land purchases, to which Mr Dawes said he could not remember.

Mrs Dunne pushed again, asking Mr Dawes why the agency proceeded with buying rural land when the government was seemingly focused on urban development.

Mr Dawes insisted there was "no opposition" from the government, noting that all acquisitions above $5 million had to be signed off by ACT Treasury.

He noted the agency had been presented with an unsolicited, four-page report from real estate agents Colliers International which proposed the government buy blocks of land around Stromlo.

Private developers were also eyeing land in the area, hastening the need for the government to secure available properties, Mr Dawes said.

He said the deals meant that future governments would have options to either redevelop the blocks, maintain them as environmental zones or, as a last resort, re-sell them as rural land.

"One of things that we need to remember in all of this is that we acted in a way of ... trying to bulletproof the territory for future land," Mr Dawes told the committee.

The committee also questioned Mr Dawes on the agency's handling of a deal involving a rural property called Fairvale.

The audit report last year found the agency had intended to purchase the property, but later supported its subdivision so that valuer Steve Flannery could buy part of the block.

The report queried the agency's decision, given it meant the government would not be able to purchase the entire property.

The parcel of land it did acquire might also be less suitable for redevelopment.

Asked on Wednesday to explain the agency's action, Mr Dawes said the board believed it was better to secure a portion of the block than none at all.

Mrs Dunne hit back, claiming the agency was, at one point, in a position to negotiate to buy the entire block.

Mr Dawes rejected that assertion.

"You can quiz me as much as you like," he said. "We bought what was on offer."

Mr Dawes now works as a private consultant and lobbyist. Mr Stewart is the director of planning and development at Canberra construction giant Geocon.

During the afternoon's hearings, the agency's former chief financial officer, Anita Hargreaves, revealed she was not kept informed, or consulted, on the land deals.

Ms Hargreaves said that would have only occurred if there had been "anomalies" or other budgetary concerns.

She said the agency was travelling "very, very well" financially before it was abolished in July 2017.

The inquiry is scheduled to hold another public hearing next week.