It follows a unanimous decision from the UK Supreme Court in April on how a woman should be defined in law.
Judges ruled at the time that the definition of a “woman” and “sex” in the Equality Act 2010 refers to “a biological woman and biological sex”.
Confirming the “extremely painful” decision, chief executive Melissa Green said: “It is with the utmost regret and sadness that we must announce that from April 2026 we can no longer offer formal membership to transgender women.
“As an organisation that has proudly welcomed transgender women into our membership for more than 40 years, this is not something we would do unless we felt that we had no other choice.”
Ms Green said that in order to “be able to continue operating as the Women’s Institute, a legally-recognised women’s organisation and charity, we must act in accordance with the Supreme Court’s judgment and restrict formal membership to biological women only”.
She added: “This change is only in respect to our membership policy and does not change our firm belief that transgender women are women.”
The NFWI said while it can no longer “legally offer formal membership to transgender women”, it will “bring forward programmes to continue to extend fellowship, sisterhood, and support to transgender women”.
Founded in 1915, it is the UK’s largest women’s organisation, with 70 federations across the country.
The NFWI said it does not hold data on how many of its members are transgender.
On Tuesday, Girlguiding, the UK’s largest youth organisation for girls, also announced it would ban transgender girls from joining following the ruling.
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The policy changes come as organisations are still waiting for new transgender guidance produced by the Equality and Human Rights Commission (EHRC) following the verdict, which is being assessed by the government.
Ministers have had the guidance for three months, but vowed not to “rush” publication of a proposed code of practice which will be used by businesses and other organisations.
The guidance, which informs the provision of single and separate-sex services such as toilets and changing rooms, requires ministerial approval.
It would only come into force 40 days after the government had laid the draft code in parliament.
The EHRC wrote to the women and equalities minister in October urging her to hurry up with bringing in the new guidance, saying some organisations were currently using unlawful practices.
