Mrs. Macron’s style has always skewed less-is-more. Judging by her public appearances since they began working together this year, Mr. Barthelat’s influence has been both subtle and significant.

The first lady has been loyal to Louis Vuitton, wearing designs by its artistic director, Nicolas Ghesquière, a friend whose runway shows she attended before becoming a public figure. Other classic French names in her wardrobe include Balmain, Courrèges and Dior.

But recently she has also taken to wearing sharp jackets by lesser known designers and labels: Alexandre Vauthier (in red or black), Stéfanie Renoma (powder blue) and the tailoring specialist Pallas (beige, at the G20 meeting in July in Hamburg, Germany), the better to cast a halo around a larger group of French names.

And it’s not just about high fashion. Jewel-neck tops and other separates by midrange French brands like ba&sh, Sandro, Georges Rech and Paule Ka have appeared in the mix. On a state visit to Greece in September she was spotted wearing a Greek-coin “Profile” ring by Marc Auclert, whose designs incorporate antique artifacts and who is one of the few designers willing to discuss the effect of her favor.