Seven years ago, Mark Zuckerberg, the chief executive of Meta, testified for the first time in Congress. After a two-week boot camp by his lawyers to prep him, he answered questions in three back-to-back-to-back hearings over two days in a baptism by fire.

Mr. Zuckerberg, 40, has had even more practice since then. He has appeared before Congress eight times and testified in court at least twice, more than any of his peers at the biggest tech companies. He has defended his company, previously known as Facebook, on issues such as privacy, child safety and the spread of disinformation.

As early as Monday, Mr. Zuckerberg will again take the hot seat, this time as the marquee witness in the Federal Trade Commission’s landmark lawsuit accusing Meta of breaking antitrust law. Regulators sued the company in the U.S. District Court for the District of Columbia over its acquisitions of Instagram and WhatsApp, saying it used a “buy-or-bury strategy” to maintain a monopoly in social media.

Mr. Zuckerberg’s turn as a serial witness has become a potent symbol of Washington’s growing frustration with the power held by Silicon Valley, fueling attempts to rein in the tech industry. Under President Trump, tech chief executives have cozied up to the administration in hopes that regulators will take a softer hand, but so far his appointees have signaled continued scrutiny.

On Capitol Hill, lawmakers have railed at Mr. Zuckerberg, accusing him of lying and having personal responsibility for various societal harms. Previous tough questioning could help him during his expected seven hours of testimony defending Meta in the antitrust trial, legal experts said.

“He seems to be much more aware of the audiences he’s speaking to compared to his earlier years,” said Adam Sterling, associate dean at Stanford Law School. “Whether it’s a deposition or a lawsuit or in front of the Senate, he can actually craft the message to the recipients of it.”