Signal, the encrypted messaging app, appoints a president.

Signal, the encrypted messaging app, has tapped Meredith Whittaker, a former adviser to the Federal Trade Commission chair and an artificial intelligence expert who protested Google’s use of the technology for military projects, as its president.

In the newly created role, Ms. Whittaker will guide policy and strategy for the messaging app and work to expand Signal’s business.

Signal, which is committed to its users’ privacy, does not know how many people use the app, although the number appears to be growing. The app has been downloaded more than 100 million times from the Google Play store, and it ranks 15th among social networking apps on Apple’s App Store.

The switch from text messaging to secure apps like Signal is part of “a growing public awareness over the past half-decade of the harms and reality of the big tech surveillance business model,” Ms. Whittaker said in an interview. That awareness, she added, has led people to “make choices that reject that business model and work to preserve their privacy.”

Signal, which started in 2014 and attracted privacy-minded users from Silicon Valley, has grown into a mainstay messaging app. The service is free. Unlike other free apps, Signal has never raised venture capital funding or sold advertising.

The nonprofit that maintains Signal is funded by donations — most notably, a $50 million infusion in 2018 from Brian Acton, the co-founder of WhatsApp who is Signal’s interim chief executive. (Mr. Acton left WhatsApp, which is owned by Meta, in 2017 and has become a vocal critic of Meta.) Signal also collects donations from users, rewarding contributors with badges that they can display on their profiles.

“Brian’s contribution helped lay a foundation where we have the room to work toward a broad base of support that sustains Signal for the long term,” Ms. Whittaker said. “It costs tens of millions of dollars every year to maintain Signal, and that’s a very lean budget compared to our competition.”

Compared with the hundreds of people working on WhatsApp, Signal employs around 40 people.

Ms. Whittaker, who did not provide her age, worked at Google as an artificial intelligence researcher for more than a decade. In 2018, she protested the company’s involvement in Project Maven, a military project that used artificial intelligence to interpret images gathered by drones, and its $90 million payout to an executive accused of sexual harassment.

She left Google in 2019 and has since advised the F.T.C. chair, Lina Kahn, on artificial intelligence issues and researched artificial intelligence and ethics as a professor at New York University.

Ms. Whittaker said she planned to focus on policy as Congress weighs a bill that could require companies like Signal to break encryption and scan the contents of users’ messages.

“To keep our privacy promises,” she said, “we need to keep our privacy designs robust.”