NEW YORK TIMES | VANESSA FREIDMAN

Christian Dior has finally found its designer.

In a move that will break up one of the most feted design teams in fashion, Maria Grazia Chiuri of Valentino is expected to be named artistic director of Dior, becoming the first woman to lead the brand in its 70-year history.

The move, which is expected to be announced next month, has the potential to disrupt the luxury fashion landscape as Ms. Chiuri, now co-creative director at Valentino, parts ways with her longtime collaborator, Pierpaolo Piccioli.

The news, reported earlier by Reuters, broke just a day after the Valentino men’s wear show in Paris and hours after Ms. Chiuri hosted a dinner in the city at Caviar Kaspia, on Place de la Madeleine, with Mr. Piccioli in celebration of the collection.

Both Dior and Valentino declined to comment, but a person briefed on the negotiations confirmed the appointment.

“I think it’s nothing short of a brilliant appointment,” said Robert Burke, founder of his own luxury consultancy. “It makes perfect sense from both an aesthetic standpoint and a consumer standpoint. There are few brands that compete with Dior, but Valentino is one.”

Ms. Chiuri and Mr. Piccioli were appointed co-creative directors at Valentino in 2008, staying at the Italian fashion house when it was sold by the private equity group Permira to the Qatari-controlled Mayhoola for Investments in 2012. Together they brought Valentino to billion-dollar status, making it a darling of both the fashion and celebrity worlds in the process.

Annual sales have more than quadrupled, to 987 million euros, since 2009 as Ms. Chiuri, Mr. Piccioli and Stefano Sassi, Valentino’s chief executive, led an expansion of the brand’s product range and distribution. And after it nearly doubled its profit on revenue of more than $1 billion in 2015, there has been growing speculation in the luxury industry about an initial public offering of stock.

The fashion house said this year that it expected revenue to grow at a double-digit pace in 2016, and it has plans to open about 25 stores globally. The company now operates 130 shops directly and is aiming for about 200 in the next two to three years.

The Dior appointment will be Ms. Chiuri’s first solo design post and will leave Mr. Piccioli alone at the creative helm of Valentino.

Ms. Chiuri originally hired Mr. Piccioli to work with her in the accessories department of Fendi in 1992, and the two have moved in tandem since then. They have been professionally so intertwined that they often finish each other’s sentences, co-sign handwritten letters, send emails from the same account and dress alike in matching black trouser suits.

“I always thought of them as a team, not as individuals. The big question is whether they can do separately what they did together,” said Mr. Burke. “That’s the risk.”

Scott Schuman, a photographer known as “The Sartorialist” who worked in a wholesale showroom that sold Valentino early in his career, said, “I am interested to see how they play on their own.”

He continued: “A lot of the high-end couture labels seem like golden cages. The sensibility I understand for her, she’ll create clothes you can buy and wear — not just accessories.”

Ms. Chiuri will be joining Dior at a delicate time. The luxury market is expected to grow only 2 percent this year, according to a study from Bain & Company and Altagamma, the Italian trade association.

Dior has been designer-less since October, when its artistic director, Raf Simons, left the company after three years. Mr. Simons had been appointed after the firing of John Galliano, who had been accused of a drunken anti-Semitic rant. Mr. Simons was credited with not only modernizing the Dior aesthetic, but also restoring an internal calm to the fashion house. His departure threw it into limbo once again.

Rumors that Ms. Chiuri was being considered for the artistic director position had been circulating in the fashion world since the beginning of the year. However, the job has traditionally involved only women’s wear and not men’s wear, designed by Kris Van Assche; jewelry, designed by Victoire de Castellane; or retail, designed by Peter Marino, and it was viewed as difficult to fill. This had to do with both its demands — six collections a year, including Cruise collections in exotic locations — and its limitations, including the involvement of celebrity ambassadors.

Mr. Simons, for example, was said to be particularly upset to discover he had not been consulted on the signing of Rihanna as a Dior face, given the gulf between the aesthetic he had established for the brand and that of the pop star.

The parent company of Moët Hennessy Louis Vuitton, Dior is the cornerstone of the luxury empire built by Bernard Arnault, its chairman and chief executive. Though it reported more than €5 billion in sales last year and has 195 stores worldwide, three-fifths of its revenue came from perfumes and cosmetics. Christian Dior Couture, which includes all the clothing lines, contributed €1.8 billion to sales in 2015.

Recent shows created by the internal design team led by Serge Ruffieux and Lucie Meier have been met with tepid applause, and Dior’s fashion sales growth has fallen in the last 18 months, going from double-digit growth to flat in the first quarter of 2016. A dip in tourist numbers to Europe after terror attacks in Paris and Brussels and sales declines in several crucial Asian markets contributed to the losses. Ms. Chiuri will be charged with reversing that trend.

In Paris, Pamela Golbin, chief curator of fashion and textiles at the Musée des Arts Décoratifs, noted Ms. Chiuri’s long successful track record and willingness to grow.

“She does have an incredible knowledge of haute couture, and that’s going to be a very important aspect of her job,” Ms. Golbin said. “There aren’t that many people who have shown over a long period of time that they could take it to the next level and have it evolve. She’s done that over the years at Valentino. What will happen at Dior is a big question.”

The next couture season, scheduled for the week of July 4, will herald Ms. Chiuri’s final show with Mr. Piccioli. A new era for Dior, Valentino and their designers will begin in September with the women’s ready-to-wear shows.