NSW Greens senator Lee Rhiannon has quit federal parliament to allow her replacement, Mahreen Farqui, to get used to the job before a tough 2019 election campaign.

NSW Greens senator Lee Rhiannon has announced she's quitting her seat in mid-August to make way for NSW MLC Mehreen Faruqi.

The senator announced her early retirement on Facebook, saying she will be finishing up 10 months before her term is due to expire in mid-2019.

"I warmly congratulate Mehreen and look forward to assisting with the coming state and federal election campaigns," she said.

Lee Rhiannon has announced her retirement. Alex Ellinghausen

The senator said her time in Parliament had been "fruitful", and she remained "passionate and as committed as ever to our collective struggle for a fair, just, ecologically sustainable and peaceful world."

"In some ways I am an accidental politician," she said.

"When I was young, Parliament was where we went to protest, not to get a job. My years as an MP have strengthened my belief that it is people’s action that drives progressive social change."

Senator Rhiannon said it had been "a pleasure and an honour" to work as a Greens MP, and thanked her staff, activists, unions and community groups for their support.

She signed off: "See you in the streets."

It ends a long and turbulent stint in politics for Senator Rhiannon.

Earlier in the year, the senator faced an internal push for her to quit Parliament before the next election.

Senator Rhiannon was met with a proposal in April from NSW Greens members who wanted her to work on a "transition plan", aimed at giving Dr Faruqi the best chance of winning the seat at the next federal election.

Taking over: Dr Mehreen Faruqi. Max Mason-Hubers

The proposal was sent to the party's 4000 members and, while she did not comment publicly, Senator Rhiannon slammed the campaign in a post to the party's internal forum.

"I am concerned and offended by this proposal and the actions associated with it," she wrote.

"I am committed to Mehreen being elected to the Senate, despite insinuations to the contrary."

The push for the senator to quit early came after she was defeated by Dr Faruqi in a November preselection ballot to be the lead Senate candidate at the next federal election, winning 60.7 per cent of the vote.

At the time, Dr Faruqi thanked Senator Rhiannon for all the work she had done for the Greens.

"I've had the privilege of working with her and it's been a great partnership on the issue of womens' right, inequality and many others," she said.

The loss was seen as a blow to the left faction of the party, which she lead for a number of years.

In June last year, the senator was temporarily suspended for opposing the federal government's Gonski 2.0 funding package, as Greens Leader Richard Di Natale was attempting to negotiate with the government to pass it.

Lee Rhiannon, right, at the Pine Gap peace camp in 1983. Supplied

Senator Rhiannon had authorised a leaflet, that claimed the Turnbull government's plan would strip funding from public schools.

Senator Rhiannon has been a Greens senator for NSW since 2011 after winning a seat in the 2010 federal election.

Before that, she was a Greens member of the Legislative Council in NSW from 1999 to 2010.

Senator Rhiannon was formerly a member of the Communist Party of Australia and later the Socialist Party of Australia, leaving the latter in the early 1980s, and joined the Greens in 1990.

In her time as a political activist, she organised a peace camp protest at the Pine Gap defence facility in 1983.