Pro-smackers be warned - Sue Bradford may be leaving Parliament, but she will not give up on her crusade.

Ms Bradford, 57, yesterday vowed to make sure her "anti-smacking" legislation led to an embedded change in New Zealand parenting and attitudes towards children.

She acknowledged the law would continue to be attacked, but said she did not consider staying on as an MP to protect it.

"If I waited for the Section 59 debate to be resolved, I might be here until I'm 93," she said.

Ms Bradford's shock resignation is a result of her disillusionment with politics after losing her bid for the Greens co-leadership.

The loss, to Metiria Turei, It made her question where her energies might be best spent.

"I've seen too many MPs in Parliament who are here but their hearts aren't in it, or they are time wasting, or they just wanted the salary. I've never wanted to be that kind of MP."

During her decade in Parliament, Ms Bradford was consistently rated one of its best MPs. She had three member's bills passed; some MPs never acchieve one.

She was the Herald's backbencher of the year in 2000 after defying predictions that the veteran protester would be a fish out of Parliament's conformist waters and in 2007 after the smacking amendment was passed.

Highly focused and effective behind the scenes, she was not a grandstander like some of her colleagues.

Politicians on both sides of the House enjoyed dealing with her and expressed dismay yesterday at her departure.

Ms Bradford was clear yesterday about her greatest achievement - removing the defence of reasonable force for the purpose of correction in her smacking reform.

It shifted the way Parliament and New Zealanders viewed children, she said.

"Even now John Key is standing up and saying, no, we are not bowing down to those who want the right to again legally hit their kids with implements," she said yesterday.

Ms Bradford will leave at the end of October and be replaced by Aucklander David Clendon, an adviser with the Sustainable Business Network.

She hopes to return to activism, saying: "Make no bones about it. I'm still a radical despite my 10 years here."

She would also look to do academic work, and as a trained journalist perhaps a newspaper column or radio show.

Any spare time could be dedicated to her hobby, fishing. "I was the only fisherman in the Green caucus."

* "Anti-smacking" law.
* Making the minimum wage apply to 16 and 17-year-olds.
* Law letting mothers in jail keep their babies for longer.
* Government spokeswoman on Buy Kiwi Made campaign 2005-08.