Deal or no deal, Ms. Falque-Pierrotin is in a position to play a major role. If negotiators agree to a new pact, she and Europe’s other privacy watchdogs will help decide whether the new agreement meets the region’s tough standards. If no deal is reached, she could impose further restrictions on how data is transferred across the Atlantic when European regulators gather on Feb. 2.

“The French aren’t afraid to pick fights with companies,” said Max Schrems, an Austrian law student who brought the original case that upended the previous trans-Atlantic data-sharing agreement.

Ms. Falque-Pierrotin follows a long tradition of French officials promoting strict privacy rights. In 2014, her peers elected her to lead an increasingly powerful group of European privacy regulators — a position that she is the forerunner to retain when new elections take place next month.

After receiving degrees from some of France’s top business and civil service schools, Ms. Falque-Pierrotin has spent three decades leapfrogging among government agencies and state-sponsored nonprofits. In the late 1990s, though, she began focusing more on privacy and the digital economy. She joined France’s data-protection authority in 2004 and quickly rose within its ranks.

In person, Ms. Falque-Pierrotin comes across as soft-spoken and formal. But her advocates and targets alike say she can be tenacious, though fair-minded. In recent years, she has gained a reputation for taking on some of the world’s largest tech companies, including Google.

The search giant will again take center stage in the coming weeks when France’s data-protection watchdog is expected to fine the company for failing to comply with its interpretation of Europe’s “right to be forgotten” privacy ruling, according to two people with direct knowledge of the matter, who would speak only on the condition of anonymity. While such a move is a headache for a company like Google, the agency’s one-off maximum financial penalty of 150,000 euros, or about $160,000, is essentially a mere rounding error.