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.
The UK economy grew by 0.1% between July and September, according to the Office for National Statistics (ONS).
However, despite the small positive GDP growth recorded in the third quarter, the economy shrank by 0.1% in September, dragging down overall growth for the three month period.
The growth was also slower than what had been expected by experts and a drop from the 0.5% growth between April and June, the ONS said.
Economists polled by Reuters and the Bank of England had forecast an expansion of 0.2%, slowing from the rapid growth seen over the first half of 2024 when the economy was rebounding from last year’s shallow recession.
And the metric that Labour has said it is most focused on – the GDP per capita, or the economic output divided by the number of people in the country – also fell by 0.1%.
Reacting to the figures, Chancellor of the Exchequer Rachel Reeves said: “Am I satisfied with the numbers published today? Of course not. I want growth to be stronger, to come sooner, and also to be felt by families right across the country.”
“It’s why in my Mansion House speech last night, I announced some of the biggest reforms of our pension system in a generation to unlock long term patient capital, up to £80bn to help invest in small businesses and scale up businesses and in the infrastructure needs,” Ms Reeves later told Sky News in an interview.
“We’re four months into this government. There’s a lot more to do to turn around the growth performance of the last decade or so.”
The sluggish services sector – which makes up the bulk of the British economy – was a particular drag on growth over the past three months. It expanded by 0.1%, cancelling out the 0.8% growth in the construction sector.
The UK’s GDP for the most recent quarter is lower than the 0.7% growth in the US and 0.4% in the Eurozone.
The figures have pushed the UK towards the bottom of the G7 growth table for the third quarter of the year.
It was expected to meet the same 0.2% growth figures reported in Germany and Japan – but fell below that after a slow September.
The pound remained stable following the news, hovering around $1.267. The FTSE 100, meanwhile, opened the day down by 0.4%.
The Bank of England last week predicted that Ms Reeves’s first budget as chancellor will increase inflation by up to half a percentage point over the next two years, contributing to a slower decline in interest rates than previously thought.
Announcing a widely anticipated 0.25 percentage point cut in the base rate to 4.75%, the Bank’s Monetary Policy Committee (MPC) forecast that inflation will return “sustainably” to its target of 2% in the first half of 2027, a year later than at its last meeting.
The Bank’s quarterly report found Ms Reeves’s £70bn package of tax and borrowing measures will place upward pressure on prices, as well as delivering a three-quarter point increase to GDP next year.