Labor and Liberal members united to significantly alter the territory's electoral landscape for future polls, with eight new members to be returned in addition to the existing 17.

The ACT Greens supported the increase, while vehemently opposing a move to five member electorates which they described as an "electoral stitch-up".

Minister Shane Rattenbury said the smaller electorates would make it harder for independents and minor parties candidates to win, lifting the required quota to 16.6 per cent of the vote.

A four-person redistribution committee will be established by the ACT Electoral Commission by October, charged with creating five new territory electorates.

ACT Chief Minister Katy Gallagher said the expansion was required because of significant population growth since the Assembly was first established.

"MLAs are serving electorates that are a lot larger than they were back in 1989 and ministers are dealing with a lot more complexity in their workload and a lot more expectation from the community about their ability to oversee a whole range of functions," she said,

"There will be many people who will see this as an opportunity to stand, where they don't have to knock off an existing candidate if they don't want to, as there's another eight seats for which there will be vacancies."

Ms Gallagher and Opposition Leader Jeremy Hanson indicated broad candidate selection processes could formally begin after Tuesday's vote.

Candidates for party preselection, including Liberal James Milligan, will soon begin their long run to 2016.

Mr Milligan – a Gungahlin small business owner who has previously stood at ACT and federal elections – said the changes would lead to better representation of local communities.

"The current Molongolo electorate runs from Gungahlin, through city Canberra, down to Weston Creek and it includes a vast number of issues, compared to those in smaller areas like Gungahlin.

"I have a good feeling about my chances to be preselected and I will certainly be seeking to represent the issues of Gungahlin and aiming to push towards a change of government," Mr Milligan said.

He said all candidates would be able to run more effective campaigns and the changes would improve the territory's governance.

"Currently the community is under-represented through our Assembly, especially in comparison to other states and territories. The workload that ministers face, having multiple portfolios, means some areas might not receive the attention they deserve."

Ms Gallagher said a ministry of eight or nine members could be required and that a working group would be established inside the Assembly to consider administrative arrangements, including required changes to ministerial office accommodation to allow for a larger backbench contingent.

Temporary office space may be required, while the taxpayer will spend well over $6 million extra each year for the expanded chamber.

The cost for staffing and salaries of backbenchers totals more than $410,000 while ministers cost more than $1 million annually.

Mr Hanson rejected suggestions the five electorate model had been chosen to edge out minor party candidates. "The Greens want a certain number that favours the Greens. I think the five members will provide for better representation on the ground.

"What I'd say to people is get on board and join any of the parties, Liberal, Labor or Green," he said. "If you are interested in democracy, if you want to make a difference in Canberra, this an opportunity to do that," he said.

Mr Rattenbury said diversity and effective community representation would be more difficult after 2016.

“The Legislative Assembly is a better place when we have a range of representatives from different backgrounds who put new ideas and thoughts on the table, challenge established ideas and encourage us to rethink how we govern.

“I believe that the people of the ACT would have been better served by electorates of between seven and nine members and that the benefits to our community should have been the focus of this debate, not the benefits to any particular party."