WASHINGTON — One of Lina Khan’s first projects as a new staff member at an antitrust think tank in 2011 was researching the history of the market for books, which had increasingly been dominated by Amazon. It was an early, unpublished entry in a body of work that has since established her as a major critic of the tech giants and corporate concentration.

She spent the next 10 years honing her arguments, becoming a leading figure in a growing movement that calls for more aggressive policing of Google, Facebook, Apple and Amazon.

Now she’s in a position to put those ideas into action — and in doing so, potentially reshape how the country regulates its biggest companies. On Tuesday Ms. Khan, 32, was sworn in as chair of the Federal Trade Commission after being appointed to the role by President Biden, the youngest in the agency’s history and its most progressive in at least a generation.

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“She is extremely humble,” said Sarah Miller, the director of the American Economic Liberties Project and a former co-worker of Ms. Khan’s who supports her approach to antitrust. “She is focused on ideas and strong arguments.”