The branch has also distanced itself from comments made by party elder Bob Brown, who criticised the victim for not going to the police soon enough.

The admission follows the party bungling the handling of the allegation, including a former party convener attempting to water down an internal report of an investigation into the allegations.

The former Greens volunteer alleged that on the night of the 2016 election, a male Greens volunteer held her down in the back of a taxi, told her he hated her and digitally penetrated her.

It is one of three allegations of sexual misconduct where former staffers or party volunteers claimed their complaints were mishandled by various branches of the party, and which, after airing on ABC's 7.30 about two weeks ago, have led to a number of Young Greens resigning from the party in disgust.

Since the allegations first aired in July 2017, the ACT political party has been quiet about the allegation and the reported mishandling of the woman's complaint, saying it was dealing with a legal issue related to the complaint.

The party's convenor, Emma Davidson, who was not convenor at the time, has said the party had reached a financial settlement with the complainant, but the terms of the settlement were confidential.

She said now the legal issues were resolved, the party could publicly release a statement, which was uploaded to the party's website this morning.

In the statement, the party admits to "serious errors in the ACT Greens' complaint handling resulting in significant harm to those involved".

It was previously revealed in emails obtained by Fairfax Media, a former party convenor tried to water down a report into problems from the 2016 campaign, including removing references to three critical incidents that occurred, though the former convenor's suggested changes did not make the final report.

The party also faced claims it had no formal mechanism for party members or volunteers to make complaints and no capacity to professionally handle the woman's complaint when it was first made.

Lawyer Rory Markham, who represented the ACT woman and other complainants in Victoria and NSW, and spoke to 7.30, told the program it seemed the party's attitude broadly was one of "absolute dismissiveness and to maintain party brand at all costs".

But ACT Greens leader Shane Rattenbury said the party had no tolerance for sexual assault or any other harassment or bullying, and while he referred detailed queries to the branch, he said the party was working hard to address the problems.

Former Greens member and whistleblower Zach Ghirardello said the admission of responsibility was a "good step" but "countless others are yet to receive this treatment or response".

"They're yet to acknowledge or apologise for other incidents arising from the result of the 2016 election. Those responsible [for the bungle] continue to be in a position of influence in the party," Mr Ghirardello said.

He pointed to a job ad for a new campaign manager, posted on Ethical Jobs last week, which omitted in its key competencies any human resources training or the need for a Working With Vulnerable People check.

"It's like they're saying one thing and doing another," Mr Ghirardello said.

The ACT Greens statement said the party acknowledged it had a duty of care to volunteer and paid staff and it was committed to providing a safe environment for all its members.

"The ACT Greens acknowledge that their past policies and procedures have not adequately protected vulnerable members of the community who assist and volunteer with them," the statement reads.

The party also said it did not endorse comments made by former federal Greens leader Bob Brown that criticised the ACT complainant for not reporting the assault to police soon enough, and "the ACT Greens condemns victim-blaming of sexual assault survivors".

“The crime in the presence of a third person sympathetic to the victim, should have been immediately reported to the police. Inexplicably, your adult, articulate and anonymous correspondent did not do so for many months," Mr Brown wrote in a letter in response to an article published by the Saturday Paper.

That article was written by the victim, but her identity was protected.

Mr Ghirardello said Mr Brown's comments were "disgusting", but while the ACT Greens had distanced themselves from him, the national branch "still rolls him out wherever they can".

The ACT party said since the 2016 federal election campaign it was now training staff and volunteers in how to manage workplace bullying and sexual harassment, with the first group trained in February this year.

All ACT Greens volunteers will now also have to agree to sign on to a volunteer code of conduct before working for a party campaign, with a second code of conduct for members, and a management committee with formal authority to ensure members adhered to it.

The party in October last year also endorsed a new constitution, including an arbitration and conciliation committee that is tasked with hearing and attempting to resolve complaints before they escalated, a committee which operates at arms length from the management committee.

The party is also currently appointing "wellbeing officers" as an initial contact for volunteers needing support or advice, and a new online form for volunteers or staff to report health and safety incidents, while new resources would be produced and given to volunteers on campaigns.

It has also secured "the right insurance policies to cover staff, volunteers and directors for future campaigns".