Ms Bradford recently lost a contest for the party's co-leadership to Metiria Turei, after Jeanette Fitzsimons stood down.
That prompted her decision to leave, effective from October 30.
It was too early to be making decisions about the future but running for the super city council was a possibility, she said.
"I wouldn't completely write it off. There's a possibility," she told The New Zealand Herald.
Manukau mayor and super city mayoral candidate Len Brown said Ms Bradford would make a great councillor, he enjoyed her company and she was totally genuine.
Ms Bradford said she had had a tough four months. "I have spent the time since then thinking very deeply about my future.
"I'll always be politically active and Parliament is just one vehicle for political change. I'll be going back to the grassroots."
Green Party co-leader Russel Norman said the party would have liked Ms Bradford to stay, but respected her decision.
Council of Trade Unions president Helen Kelly said Ms Bradford would be "hugely missed" by the union movement.
Barnardos New Zealand said Ms Bradford's work in Parliament had been outstanding.
"Her imminent departure is a significant loss for the people she so effectively represented," said chief executive Murray Edridge.
Labour leader Phil Goff said Parliament was losing a strong and passionate advocate for low income workers, unemployed people, beneficiaries "and other people who might get a raw deal".
The Green Party's new MP will be Aucklander Dave Clendon, a sustainable business adviser.
