Ann Sarnoff attends the 32nd Annual WP Theater's Women of Achievement Awards Gala at The Edison Ballroom on March 27, 2017 in New York City.

Ann Sarnoff has been named CEO and chairwoman of Warner Bros., according to an internal memo from John Stankey, the head of WarnerMedia.

Sarnoff most recently served as the president of BBC Studios Americas.

"Ann is a recognized strategist and respected leader of diversified businesses, with a proven track record of driving growth, innovation and consumer engagement," Stankey said in the memo obtained by CNBC. "Her experience spans media, entertainment, digital product development, consumer products, licensing and distribution, in leadership roles with companies from Viacom and Dow Jones to the WNBA and PayPal."

Shares of AT&T, which owns Warner Bros., remained relatively unchanged in midday trading.

"I'm excited to work with Bob [Greenblatt] and Kevin Reilly to flesh out the plans for the streaming services," Sarnoff told CNBC's Julia Boorstin. "Warner has a lot to offer in that regard."

Sarnoff's predecessor, Kevin Tsujihara, exited the company in March amid an inappropriate relationship with an actress.

Tsuijhara, 54, had been with the WarnerMedia unit for more than 24 years. He became CEO in early 2013 and chairman later that year. Tsuijhara, the first executive of Asian decent to head a major Hollywood studio, led Warner Bros. to have its most profitable year ever in 2017.

However, also under Tsuijhara's tenure, Warner Bros. struggled to produce DC superhero films at the same caliber of its counterparts at Disney and Marvel Studios. It wasn't until 2017′s "Wonder Woman" that the studio found true success, taking in $821 million in ticket sales worldwide. A year later, "Aquaman" became the first DC film to cross the $1 billion mark.

After first announcing a deal to acquire Time Warner in 2016, AT&T closed the merger in June 2018. With Tsuijhara's departure, all of the management that joined AT&T from Time Warner is now gone.

Jeff Bewkes, former CEO of Time Warner; John Martin, former CEO of Turner and Richard Plepler, former CEO of HBO, have all departed the company in the last year.

Here is the full internal memo: