Mr Barr and Greens leader Shane Rattenbury inked the deal on Monday, following negotiations between the two parties in the wake of the October 17 ACT election.

The deal means the Greens will support Labor to form government for the next four years.

The Greens' record haul of six seats at the election has been rewarded, with Mr Barr agreeing to appoint three members of Mr Rattenbury's team to the ministry.

Mr Barr will unveil his new ministerial lineup on Tuesday, which was expected to include Tara Cheyne in place of Suzanne Orr.

The Canberra Times understands Ms Orr's demotion was confirmed at Monday's Labor caucus meeting, with the move believed to have angered some members of the party's left faction.

Mr Barr refused to confirm Ms Orr's expected demotion when he fronted reporters on Monday afternoon.

After playing down the prospects of multiple Greens in cabinet in the days after the election, Mr Barr said the "iron law of mathematics" meant Labor's junior governing partner had claims to three ministerial positions.

Mr Barr said the new Greens members would be allocated minor portfolios, in an expanded nine-member cabinet.

"They won't be the two most senior ministers in the government, I can tell you that," he said.

"They will have important roles, but I'm not expecting people who have just been elected to take on senior portfolios."

The so-called parliamentary and governing agreement includes a suite of items the Labor-Greens government has committed to delivering in the next four years, across areas including climate action, planning and housing, gambling harm and light rail.

While the two parties have been forced to compromise on a number of the policy positions they put to voters ahead of the ACT election, both leaders were pleased with the final agreement.

"This is about putting together an agenda for the next four years to provide a stable government with an ambitious program to respond to the issues of this city," Mr Rattenbury said.

"Canberrans want us to come together and get on with governing ... that's what this is all about."

Mr Barr said the agreement reflected the shared values of the two parties.

"Over the previous two terms of government, Labor and the Greens have demonstrated a capacity to work together to deliver stable government. There is clear support in the community for this model, and both parties remain committed to it," he said.

The government will stick with the planned 2045 target for phasing out natural gas, despite the Greens' calls for it to be brought forward five years.

But Labor has agreed to expand its $150 million household solar and battery loan scheme, allowing Canberrans to access zero-interest loans of up to $15,000 to help buy electric cars and appliances.

Under the deal, the ACT government will build a total of 400 new public housing units by 2025, an increase on the 260 originally proposed.

It will also aim to deliver an additional 600 affordable homes by the middle of the decade, as it formally acknowledged the "significant challenges in land availability, industry and sector capacity to deliver additional housing" in the ACT.

In a move likely to face opposition from the territory's community clubs, Labor has agreed to the Greens' calls for the introduction of $5 bet limits and $100 load up limits on gaming machines.

Asked if the ACT government was prepared for an industry backlash, Mr Barr said: "The short answer is yes".

"We have signed up to this with our eyes open," he said.

"We know what we are endeavoring to achieve, this has been a direction that we have been heading in. I see this as just the next step."

The changes should start rolling out by the end of 2022 at the latest, according to the agreement. It also calls for the establishment of a ministerial council, comprising club group, unions and government, to guide the industry's future.

"I don't think it needs to be a fight between the government and the clubs," Mr Rattenbury said.

"We wants this to be an orderly transition in a way that actually gets the clubs off that real addiction of poker machine money."

Labor has agreed to the Greens' request to examine the feasibility of extending the proposed Woden light rail line to Mawson.

The government will also look at the possibility of running express light rail services, despite Labor Transport Minister Chris Steel rubbishing the idea when the Greens proposed it during the election campaign.