Valentina Sampaio is one of those leggy, lush brunette models for which Brazil is famous. And it was her striking beauty and “sparkling personality,” the French Vogue editor Emmanuelle Alt said, that led her to feature the 20-year-old on the magazine’s March cover.

That, and the fact that Ms. Sampaio is transgender. “Trans people [are] the ultimate of a rejection of conformity,” Ms. Alt wrote in her editor’s letter — the sort of “icons that Vogue supports and chooses to celebrate.”

French Vogue is not the first fashion magazine to feature a transgender model on its cover. Hari Nef appeared on Frische, a twice yearly fashion and art magazine, in 2014; Andreja Peji? was on Marie Claire Spain a year ago; and Ms. Sampaio on Elle Brazil last October, to name a few. But the action was groundbreaking for the Vogue empire as well as the French fashion establishment, in part because of the cover line, “Transgender beauty: How it’s shaking up the world,” below Ms. Sampaio’s face.

Ms. Alt wrote that being transgender “is a detail one would prefer not to have to mention,” adding that Ms. Sampaio was not on the cover only for her looks “but because despite herself she embodies an age-old, arduous struggle to be recognized and not be perceived as something Other, a gender exile.”