In the piece, she criticises Sir Keir, as well as shadow home secretary Yvette Cooper, shadow equalities secretary Anneliese Dodds, shadow foreign secretary David Lammy and shadow attorney general Emily Thornberry.
Rowling has been outspoken in her belief that biological women should be able to have separate spaces, and trans women – who were born male – should not be allowed access.
She has been criticised for her position, being widely condemned in recent years for her views on transgender rights, for example claiming that she would rather go to jail than refer to a trans person by their preferred pronouns.
She added: “Grotesque transphobia, which is upsetting. I am every bit as much a woman as JK Rowling.”
Daniel Radcliffe, who became a worldwide star after playing schoolboy wizard Harry in the blockbuster adaptations of the novels, has also criticised her views, and said in an interview last month that the fallout with Rowling “makes me really sad“.
Sir Keir was asked about this statement in a recent leaders debate, at which point he said he agreed with Sir Tony Blair that women have vaginas and men have penises.
Rowling says she felt the Labour leader gave “the impression that until Tony Blair sat him down for a chat, he’d never understood how he and his wife had come to produce children”.
She added that she “really wanted to give him the benefit of the doubt”.
In her article, Rowling claims to “have been a Labour voter, a member (no longer), donor (not recently) and campaigner (ditto) all my adult life” – and she wants to see the end of the Conservative government.
According to Electoral Commission records, she gave £1m to the party in 2008, and £8,000 in 2015.
In the article, the author highlighted Ms Dodds for saying what a woman is “depends on what the context is”.
Ms Cooper is criticised for saying she was “not going to get into rabbit holes on this”.
Rowling points to Ms Thornberry for saying: “some women will have penises. Frankly, I’m not looking up their skirts, I don’t care”.
And Mr Lammy draws ire for saying women like Rowling are “dinosaurs hoarding rights”.
The Harry Potter author also claims Mr Lammy said that a cervix is “something you can have following various procedures and hormone treatments”.
Rowling wrote: “It’s very hard not to suspect that some of these men don’t know what a cervix is, but consider it too unimportant to Google.”
The NHS definition of the cervix is the opening between the vagina and the womb.
Rowling says the debate for “left-leaning” women like herself “isn’t, and never has been, about trans people enjoying the rights of every other citizen, and being free to present and identify however they wish”.
Instead, she says it is “about the right of women and girls to assert their boundaries”.
She adds: “It’s about freedom of speech and observable truth.
“It’s about waiting, with dwindling hope, for the left to wake up to the fact that its lazy embrace of a quasi-religious ideology is having calamitous consequences.”
The author says she met a mother of a girl with learning difficulties who was “smeared as a bigot and a transphobe for wanting female-only intimate care” for her.
“I cannot vote for any politician who takes issue with that mother’s words,” Rowling adds.
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She concludes: “An independent candidate is standing in my constituency who’s campaigning to clarify the Equality Act.
“Perhaps that’s where my X will have to go on 4 July.
“As long as Labour remains dismissive and often offensive towards women fighting to retain the rights their foremothers thought were won for all time, I’ll struggle to support them.
“The women who wouldn’t wheesht didn’t leave Labour. Labour abandoned them.”
Earlier in the day, Sir Keir ruled out lifting the block on the Scottish government’s controversial gender reforms.
Sky News has approached the Labour Party for comment.
Lisa Nandy has said Sir Keir Starmer’s decision to accept thousands of pounds worth of football tickets was “very sensible”.
The minister for culture, media and sport also said she had never accepted free clothes from a donor.
Speaking to Sky News at the start of the Labour Party conference today, the MP for Wigan said: “The problem that has arisen since [Sir Keir] became leader of the opposition and then prime minister is that for him to sit in the stands would require a huge security detail, would be disruptive for other people and it would cost the taxpayer a lot of money.
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“So I think he’s taken a very sensible decision that’s not the right and appropriate thing to do, and it’s right to accept that he has to go and sit in a different area.
“But I know that he’d much rather be sitting in the stands cheering people on with the usual crowd that he’s been going to the football with for years.”
Ms Nandy also said while she has not accepted free clothes – joking “I think you can probably see that I choose my own clothes sadly” – she doesn’t “make any judgements about what other members of parliament do”.
She said: “The only judgement I would make is if they’re breaking the rules, so they’re trying to hide what they’re doing. That’s when problems arise.
“Because the point of being open and transparent is that people can see where the relationships are, and they can then judge for themselves whether there’s been any undue influence.”
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She asserted there had not been an undue influence in gifts accepted by senior Labour figures, adding: “We don’t want the news and the commentary to be dominated by conversations about clothes.
“We rightly have a system, I think, where the taxpayer doesn’t fund these things. We don’t claim on expenses for them. And so MPs will always take donations, will always take gifts in kind.
“MPs of all political parties have historically done that and that is the system that we have.”
She added: “I don’t think there’s any suggestion here that Keir Starmer has broken any rules. I don’t think there’s any suggestion that he’s done anything wrong.
“We expect our politicians to be well turned out, we expect them to be people who go out and represent us at different events and represent the country at different events and are clothed appropriately.
“But the point is that when we accept donations for that or for anything else, that we declare them and we’re open and transparent about them.”
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The announcement followed criticism of Sir Keir’s gifts from donors, which included clothing worth £16,200 and multiple pairs of glasses worth £2,485, according to the MPs’ register of interests.
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Sir Keir was found to have received substantially more gifts and freebies than any other MP – his total in gifts, benefits, and hospitality topped £100,000 since December 2019.