The Supreme Court on Thursday unanimously ruled in favor of a straight woman who twice lost positions to gay workers, saying an appeals court had been wrong to require her to meet a heightened burden in seeking to prove workplace discrimination because she was a member of a majority group.

The decision came two years after the Supreme Court struck down race-conscious admissions programs in higher education and amid the Trump administration’s fierce efforts to root out programs that promote diversity. The ruling will place further pressure on employers and others to eliminate affirmative action and other initiatives that seek to provide opportunities to members of historically disadvantaged groups.

Nearly half of the federal appeals courts had required men and white people and other members of majority groups to meet a more demanding standard when they sued for workplace discrimination. In eliminating that requirement, the court said that a federal civil rights law demanded equal treatment of all individuals.

The standard for proving workplace discrimination under the law, Justice Ketanji Brown Jackson wrote for the court, “does not vary based on whether or not the plaintiff is a member of a majority group.”

The case was brought by Marlean A. Ames, who had worked for the Ohio Department of Youth Services, which oversees parts of the state’s juvenile corrections system. After a decade there, in 2014 she became the administrator of a program addressing prison rape. Five years later, she applied for a promotion.

Her supervisors turned her down, saying she lacked vision and leadership skills. They eventually gave the position to a gay woman who had been at the department for a shorter time and, unlike Ms. Ames, lacked a college degree.

Not long after denying her the new position, her supervisors removed her from her existing job, telling her that they had concerns about her leadership and offering her a demotion that came with a substantial pay cut. She was replaced by a gay man with less seniority.

Ms. Ames sued under a federal civil rights law that forbids employment discrimination based on, among other characteristics, sex. (The Supreme Court ruled in 2020 that discrimination based on sexual orientation is a form of sex discrimination for purposes of the civil rights law.)

The text of the law, Title VII of the Civil Rights Act of 1964, does not draw distinctions based on whether the person claiming discrimination is a member of a majority group. But some courts have required plaintiffs from majority groups to prove an additional element if they lack direct evidence of discrimination: “background circumstances that support the suspicion that the defendant is that unusual employer who discriminates against the majority.”

Lower courts ruled against Ms. Ames on those grounds. The U.S. Court of Appeals for the Sixth Circuit, in Cincinnati, said she could have satisfied the “background circumstances” requirement by showing that decisions about her employment were made by “a member of the relevant minority group (here, gay people)” or with statistical evidence. But the appeals court said Ms. Ames had provided neither kind of proof.