Montana Gov. Gianforte signed SB 458 defining sex as binary, eliminating legal recognition of transgender and intersex residents

On May 20, 2023, Montana Gov. Greg Gianforte signed Senate Bill 458 into law, inserting binary, reproduction-based definitions of "male," "female," and "sex" into roughly 40 sections of the Montana Code. The law defines the sexes by the presence of XX or XY chromosomes and the production of eggs or sperm "under normal development," and declares that "there are exactly two sexes." A late amendment extended the definitions to people "who would otherwise fall within" them "but for a biological or genetic condition" — language medical experts said still failed to account for many intersex residents. The law was scheduled to take effect October 1, 2023.

Drafted in part by the conservative Montana Family Foundation, SB 458 passed the Legislature earlier in 2023 largely along party lines, with the bill's sponsor, Sen. Carl Glimm, R-Kila, and other supporters framing it as a response to a rise in people identifying as transgender. Critics — including transgender lawmakers and civil-rights advocates — said the measure eliminated legal recognition of transgender, nonbinary, and intersex Montanans across state code, barring them from selecting the gender marker on their birth certificates and driver's licenses. Nonpartisan legislative analysts warned the law could jeopardize billions of dollars in federal funds tied to anti-discrimination compliance.

Updates

2023-10-12 — Residents filed suit challenging SB 458 as unconstitutional [3, 4]

A group of transgender, intersex, and Two-Spirit residents, represented by Upper Seven Law and separately by the ACLU of Montana, filed suit in state court seeking to declare SB 458 unconstitutional and permanently enjoin its enforcement, arguing it violated Montana's constitutional guarantees of equal protection, privacy, and dignity.

2025-02-18 — District court struck down SB 458 as facially unconstitutional [5, 6]

Missoula County District Court Judge Leslie Halligan granted the plaintiffs summary judgment, declaring SB 458 facially unconstitutional under the Montana Constitution's equal-protection and privacy guarantees and enjoining the state from enforcing it or similar legislation. Halligan wrote that the law "explicitly excludes" certain residents "from the definition of human beings."

2026-04-15 — Montana Supreme Court affirmed the injunction blocking SB 458 [7, 8]

The Montana Supreme Court upheld the injunction against SB 458, ruling that the state likely violated the Montana Constitution by refusing to let transgender residents update birth certificates and driver's licenses. Writing for the majority, Justice Laurie McKinnon held that "transgender discrimination is, by its very nature, sex discrimination" barred under the state's nondiscrimination clause.