Montana Gov. Gianforte signed SB 437 redefining sex as a fixed binary across state law, overriding transgender and intersex recognition

On March 24, 2026, Montana Gov. Greg Gianforte signed Senate Bill 437, a measure that redefines "sex" throughout more than 60 provisions of Montana law as a binary — male or female — determined by "primary sexual anatomy," meaning the reproductive system developed to produce either ova or sperm. The statute establishes "gender" as a synonym for that biological definition rather than gender identity, and compels transgender, nonbinary, intersex, and Two Spirit people to be designated by their sex assigned at birth on state documents including driver's licenses and marriage licenses. Sponsored by Sen. Carl Glimm, R-Kila, the bill passed the Senate in April 2025 but sat unsigned on House Speaker Brandon Ler's desk for nearly a year; Ler and Gianforte both signed it on March 24, 2026.

Gianforte said the law "codifies the long-recognized, commonsense, immutable, biologically-based definition of sex, male and female." The measure closely tracks Montana's 2023 SB 458, which defined sex as binary and was struck down as unconstitutional by a state district court that awarded attorney fees to the plaintiffs; the presiding judge had signaled that comparable measures would likely also be found unconstitutional. Advocates have said the law would force intersex and transgender residents — including a plaintiff with XY chromosomes and female genitalia who identifies as a woman — to be labeled on official records inconsistently with their identity.

Updates

2026-03-25 — Upper Seven Law moved to fold SB 437 into its pending SB 458 challenge [4, 5]

Days after the signing, the Helena-based firm Upper Seven Law moved in Montana district court to add SB 437 to its ongoing lawsuit against the 2023 SB 458, filing to bring a supplemental complaint that challenges the new statute's constitutionality.

2026-04-15 — Montana Supreme Court ruled transgender residents a constitutionally protected class [6, 7]

The Montana Supreme Court, in a 5-2 ruling in Edwards v. Montana — the SB 458 case SB 437 was added to — affirmed a district court injunction and held that the state constitution independently protects transgender residents, finding that discrimination against transgender people is inherently sex discrimination and that transgender people constitute a suspect class under Article II, Section 4. The ruling keeps the injunction in place allowing transgender residents to update birth certificates and driver's licenses and blocks enforcement of SB 458 pending trial; plaintiffs' counsel had argued there was "no substantive difference" between SB 458 and SB 437, and commentators said the decision undercuts SB 437's legal viability.