She has also revealed she will be leaving Canberra to retire to Lake Macquarie near Newcastle.

The Legislative Assembly veteran also spoke out in support of colleague Joy Burch, who resigned from the ministry this week.

Ms Porter is expected to hand her resignation to the Speaker on February 19.

That will trigger a countback by the Electoral Commission of the preferences of those who voted Ms Porter No.1 at the 2012 election.

Lawyer Jayson Hinder finished last on the Labor ticket at the 2012 election but could find himself in the Assembly by March due to the countback, with the other Labor contender, Glen McCrea, confirming he will not be contesting the position after moving to Sydney.

It will give Mr Hinder seven months to campaign and get his name known before the October 15 election.

Ms Porter, 73, who was elected in the 2004 poll, announced she was leaving politics late last year but said she would use the Christmas break to determine if she would stay until the election.

She told The Canberra Times on Thursday that her continuing battle with chronic arthritis had forced her hand and she would not serve out her term.

"I would have worked alongside my colleagues and taken a lot of the load in terms of constituents' work in my electorate. And I would have been really proud to do that and really happy to do that," she said.

"But over the break, I've realised the doctor was right. The medical advice is, 'You need to relax and do things when you want to do them. Some nice walking. Proper sleeping. And not have so much stress in your life.'

"I'm sad; I'm really sad. I feel like I'm letting my constituents down but on the other hand, I'm not because I'm letting them down at the moment by not working to my full capacity."

Ms Porter remained upbeat about Labor's chances in Ginninderra despite her retirement and the loss of her significant personal vote.

"We've got some really good candidates in Ginninderra and I think they've got very good profiles in their community. I would hope we would maintain three members in Ginninderra," she said.

She also defended Ms Burch who has dealt with a range of issues, including a cage being built in a Canberra school for a boy with autism, and her son talking to school students without the proper clearance while facing sentencing for a robbery. (ACT Commissioner for Standards Ken Crispin later cleared Ms Burch of breaching the ministerial code regarding her son's visits.)

"I think she's had a really tough time. I don't know how anyone could have withstood the strain of all of those things that happened to her," Ms Porter said.

"I saw a report in the media about the things that were controversial about her … and I thought to myself, 'A lot of that stuff they said was controversial was right outside of her control.'

"The stuff with her son, for instance, that should not be sheeted home to Joy. There's so much there that shouldn't have been sheeted home to Joy and unfortunately it has. This is the way it's been played out. The opposition like to play the guilt game.

"She needed a break from all that. I'm glad she's staying through because she has a lot to offer."

Ms Porter and her husband Ian De Landelles will in March move to Lake Macquarie, where they have built a house near the lake. She has been a resident of Canberra since 1977.

She had no qualms about starting a new life in the Hunter, saying she was used to it, moving from Britain as a child, working with remote Aboriginal communities in the Northern Territory and eventually moving to Canberra, where she helped establish what became Communities at Work in Tuggeranong.

She plans to learn to paint, spend more time with her 11 grandchildren and one great-grandchild, read more and walk more as well as volunteer, including with Greening Australia and with children in hospitals.

"It has been an enormous privilege to serve as a member for Ginninderra for more than 11 years and I wish to thank all of those who voted to elect me on three successive occasions to be their representative. I hope I have served them well and repaid them for that support," she said.