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The views expressed below are those of the authors and do not necessarily reflect those of the Carr-Ryan Center for Human Rights or Harvard Kennedy School. These perspectives have been presented to encourage debate on important public policy challenges. 

On April 16, 2025, the United Kingdom's Supreme Court issued a unanimous ruling interpreting the terms "woman" and "sex" under the Equality Act 2010 to refer strictly to biological sex assigned at birth. 

In response to this decision, we’ve gathered reflections from leading scholars in our Academic Affiliates network to provide insight into the wider consequences of the Court’s ruling. Drawing on expertise in law, human rights, and political science, these scholars help us understand the political, social, and legal stakes—both in the UK and globally.

(Royal Holloway University of London) and (University College London): 

This week’s UK Supreme Court ruling represents a significant setback for trans people. The decision defines 'sex' exclusively as the biological sex assigned at birth under the Equality Act 2010, explicitly excluding trans individuals—even those holding a Gender Recognition Certificate—from legal recognition of their gender identity (O'Thomson 2025). This decision not only permits the automatic exclusion of trans people from single-sex spaces such as schools and sports teams, but also severely restricts their ability to pursue equal pay claims. This exclusion disproportionately affects trans women and intensifies existing social and economic inequalities.

Victoria McCloud, the UK's first trans judge, characterized the ruling as occurring during "a scary time" for trans people, marking the onset of a much more intense struggle for rights (quoted in Murray 2025). Previously, the Equality Act required a “legitimate aim” to exclude trans people from single-sex spaces; now, such exclusion can occur by default. McCloud highlights the immediate, practical impacts: "If I was a trans person in the UK today, I would steer clear of using any loo in a public space unless it was a single-sex or combined-sex loo, because I personally cannot, as of this moment, judge whether I should use the male loo or the female loo" (ibid).

Critically, the Court's ruling relied extensively on arguments presented by trans-exclusive ('gender critical') activists, while notably excluding any direct input from trans voices themselves. By positioning misogyny as inherently tied to biological sex rather than the broader societal oppression long recognized by feminist movements, the decision revives problematic biological essentialism. Historically, biological essentialism was also used to exclude cis women, confining them to the domestic sphere and denying them access to education and occupations on the premise that their biology made them solely suitable for motherhood and therefore uncapable of carrying out other roles (Pateman 1988). Returning to biological essentialism, then, risks returning to periods where women enjoyed less, not more, equality relative to men.

More critically, it ignores trans women's lived realities. The judgment stands in stark tension with established human rights precedents set by the European Court of Human Rights, particularly in the landmark Goodwin v. UK ruling, which affirmed that legal gender recognition is fundamental to safeguarding trans individuals' dignity and rights (O'Thomson 2025).

References:

Murray, Jessica. 2025. "'A huge reset': trans rights campaigners and gender critical activists react to supreme court ruling." The Guardian, April 16.

O'Thomson, Jess. 2025. "UK Supreme Court Rules That Trans Women Aren’t Women under the Equality Act 2010." QueerAF, April 16.

Pateman, Carole. 1988. The Sexual Contract: Cambridge: Polity Press.

(University of Birmingham Law School):

While the Court claimed that its role in the case was merely to define who qualified as 'woman' for the purpose of the Equality Act (2010) and not to adjudicate on what has somehow become a matter of public debate, the arguments it picked certainly seem to be underpinned by particular understandings surrounding the meaning of sex. The judgement comfortably sits next to other (heteronormative) precedents, such as the one which in 2021 denied Christie Elan-Cane the possibility to obtain a 'Gender X' passport, by wielding traditional ideas of what sex ought to mean.

Once again, the idea of a 'biological' sex is brought up repeatedly by the Court as an unproblematic concept, seemingly obvious in meaning, and which allows to distinguish every born person into two neatly distinct categories. Throughout the ruling the ideas of 'biological sex' and 'certificated sex' are pitted against one another in the Court's attempt at determining which of the two is the true sex of individuals under the Equality Act. The irony that by biological sex the Court is simply meaning sex certified at birth, rather than later in life, is sadly missed in the lengthy judgment. The idea of the existence of a true immutable sex of individuals, underpinning the whole ruling, is most clearly presented in the Court's discussion about the interplay of gender and sexuality.

According to the Court: 'a lesbian must be a female who is sexually oriented towards (or attracted to) females ... This is coherent and understandable on a biological understanding of sex' (para 206). However, for the Court, the limits of sexual intelligibility are tested when gender transition is brought into the mix. The Court asserted that if a 'gender recognition certificate' (GRC) was to alter someone's gender, it would also modify their (apparently binary and fixed) sexuality. It then reasoned that, if a trans woman was to remain attracted to women after obtaining a GRC she would become a lesbian and, consequently, sexual orientation as a protected characteristic would be (seemingly) 'rendered meaningless' (para 206). Not satisfied with the logic of its argument, the Court concluded that such an understanding would carry an 'inevitable loss of autonomy and dignity for lesbians' (para. 207). It is not only worrisome that the Court could consider a whole group's autonomy and dignity to be so frail as to crumble when faced with someone else's sexuality, but it is also reminiscent of those dated arguments that claimed that LGBTQI+ people getting access to certain fundamental rights was somehow damaging to unrelated people's families and marriages.

Ultimately, the Court's decision had a sadly predictable outcome, where once again the moral panics about the threat posed to society by members of the LGBTQI+ community managed to secure a (reactionary) legal victory.

(University of Amsterdam, Harvard University):

Forward slash

Political science teaches us that institutional decisions—such as the recent UK Supreme Court ruling—often carry a legitimizing force. When institutions deemed neutral or apolitical rule against marginalized groups, their authority can reframe discrimination as reasonable and push the public toward compliance. These effects don’t stop at national borders. Reactionary movements across the globe often seize upon such decisions, treating them as legal and moral precedents to replicate. A court ruling in one country quickly becomes a strategic asset elsewhere.

But legitimacy is not the only consequence. We’ve seen time and again how progressive gains, especially around LGBTQ+ rights, have triggered organized backlash. These counter-movements do not just contest specific policies—they target the very institutions that facilitated social change, undermining their authority and mobilizing supporters around a sense of loss and grievance. In these cases, court rulings do not pacify dissent—they inflame it.

And this dynamic can cut both ways. At moments like this, when institutions move against fundamental rights, we should not accept their neutrality as given. We should name these decisions for what they are: political interventions masquerading as legal restraint. Rather than absorbing the ruling as another loss, we should transform it into a starting point. This is the potential of forward slash: a mobilized, strategic push in the opposite direction—not a reaction rooted in nostalgia, but a movement animated by solidarity and a vision for the future.

Forward slash means refusing to normalize the erosion of rights. It means recognizing that today’s anti-trans ruling is not an isolated incident, but part of a broader project to roll back hard-fought freedoms—a coordinated response that does not merely react to an unjust decision, but strategically mobilizes against it. Pro-trans and allied movements should refuse to accept the veneer of neutrality surrounding such rulings. Instead, they should expose the decision as ideologically driven and politically motivated. By doing so, they can turn this moment into a catalyst: a point of convergence for coalitions grounded in solidarity, united not only in defending trans rights but in opposing a broader authoritarian agenda that threatens the freedoms of many.

It is natural to feel anger in response to this kind of institutional violence—and research in political psychology suggests that collective anger can be a powerful engine for mobilization. If channeled strategically, it can prevent repressive spirals and build resistance instead. It can turn what was meant to demoralize into a force for political clarity.
Let us use this moment to coordinate, to speak out, and to act. Let us transform backlash into forward slash.

(Council for Global Equality):

The U.K. Supreme Court has now added junk jurisprudence to the junk science of last year's Cass Review on gender-affirming health care in Britain. Like the Cass Review, this ruling will fuel further discrimination, stigma, and violence against transgender and other gender diverse persons, notwithstanding Lord Hodge's caution "against reading this judgement as a triumph of one or more groups in our society at the expense of another." Moreover, the impact of this ruling will not be limited to the United Kingdom: we have already seen the Cass Review invoked in efforts to repeal Chile's pioneering gender identity law and to block the introduction of gender-affirming health care policies in Colombia. We will now surely see this ruling cited as the global assault on the legal rights, on even the very legal existence of transgender people marches on.

The plaintiffs in this case, For Women Scotland, were backed financially by billionaire author J.K. Rowling. For Women Scotland, Rowling, and other so-called "gender-critical" feminists are carrying the water for the anti-gender movement that uses attacks on LGBTQI+ people -- especially on transgender and gender diverse people -- as well as on sexual & reproductive health & rights and on immigrants -- as its key tool to undermine democracy, civil society, and the rule of law across the world. Like the gender-critical feminists, the anti-gender movement -- a movement backed by mega-rich Russian oligarchs, American evangelicals, and extreme-right Spanish and Latin American Catholic billionaires -- purports to be acting in defense of women and the family. This ruling will further embolden the anti-gender movement in both the Global North and Global South, though the impact will be especially dire wherever civil society is weaker and less resilient. Though For Women Scotland, Rowling, and their allies are celebrating now, this ruling takes us one step closer to a world where biology is cited to restrict the rights of all women, regardless of gender identity or expression.