Christine Shawcroft, the Labour official at the centre of an anti-Semitism row, has "resigned with immediate effect" from the party's ruling body.
The left-wing supporter of Jeremy Corbyn said her presence on the national executive committee (NEC) had become a distraction.
Ms Shawcroft was forced to stand down from her position on Labour's disputes panel on Wednesday, after she sent an email calling for a council candidate accused of Holocaust denial to have his suspension lifted.
Ms Shawcroft apologised for the email, saying she was "wrong and misguided" to have called for Alan Bull's reinstatement, and sent it "before being aware of the full information about this case" and having "not been shown the image of his abhorrent Facebook post".
Mr Bull had been due to stand in the May local elections in Peterborough, but is accused of sharing an article on Facebook which claimed the Holocaust was a "hoax". He said he reposted the article for the purpose of debate and did not agree with it.
In a statement released on Saturday, Ms Shawcroft confirmed she was standing down from the NEC "with immediate effect".
She continued: "It has been a privilege to serve on the Labour Party national executive committee for the last 19 years, and I was standing down in September in any event...
"It is clear that my continued membership of the NEC has become a distraction for the Party and an excuse for endless intrusive media harassment of myself, my family and friends...
"I reaffirm my complete opposition to anti-Semitism and my abhorrence of Holocaust denial, and support all measures to tackle this within the party.
"And I pledge my full energy to securing for our country the Labour government under Jeremy Corbyn that it so desperately needs."
It is expected that under party rules Ms Shawcroft's seat will go to comedian Eddie Izzard - the next next most popular candidate at the last NEC election - although Labour sources said they would have to account of the gender balance of the committee.
Ms Shawcroft is understood to have spoken to Mr Corbyn who backed her decision to resign and thanked her for her service.
On Friday, Labour MPs and peers sent a letter to Jeremy Corbyn urging him to suspend Ms Shawcroft.
Earlier on Saturday, deputy Labour leader Tom Watson became the most senior figure to call for Ms Shawcroft to quit, describing her claim that the whole row over anti-Semitism in the party was simply a way to get at Mr Corbyn as "disgusting".
The Labour anti-Semitism row is longstanding, but surfaced again last week after a 2012 Facebook comment Mr Corbyn made emerged in which he offered a show of support for Mear One, the painter of an alleged anti-Semitic mural that was about to be painted over.