Shortly after Jonathan Kanter took over the Justice Department’s antitrust division in November 2021, the agency secured an additional $50 million to investigate monopolies, bust criminal cartels and block mergers.

To celebrate, Mr. Kanter bought a prop of a giant check, placed it outside his office and wrote on the check’s memo line: “Break ’Em Up.”

Mr. Kanter, 50, has pushed that philosophy ever since, becoming a lead architect of the most significant effort in decades to fight the concentration of power in corporate America. On Thursday, he took his biggest swing when the Justice Department filed an antitrust lawsuit against Apple. In the 88-page lawsuit, the government argued that Apple had violated antitrust laws with practices intended to keep customers reliant on its iPhones and less likely to switch to competing devices.

That lawsuit joins two Justice Department antitrust cases against Google that argue the company illegally shored up monopolies. Mr. Kanter’s staff has also challenged numerous corporate mergers, including suing to stop JetBlue Airways from buying Spirit Airlines.

“We want to help real people by making sure that our antitrust laws work for workers, work for consumers, work for entrepreneurs and work to protect our democratic values,” Mr. Kanter said in a January interview. He declined to comment on the Google cases and other active litigation.

At a news conference about the Apple lawsuit on Thursday, Mr. Kanter compared the action to past Justice Department challenges to Standard Oil, AT&T and Microsoft. The suit is aimed at protecting “the market for the innovations that we can’t yet perceive,” he said.