President-elect Donald J. Trump is expected to name Senator Marco Rubio of Florida as his secretary of state, three people familiar with his thinking said on Monday, as Mr. Trump moves rapidly to fill out his foreign policy and national security team.

Mr. Trump could still change his mind at the last minute, the people said, but appeared to have settled on Mr. Rubio, whom he also considered when choosing his running mate this year.

Mr. Rubio was elected to the Senate in 2010, and has staked out a position as a foreign policy hawk, taking hard lines on China and Iran in particular.

He initially found himself at odds with those Republicans who were more skeptical about interventions abroad, but he has also echoed Mr. Trump more recently on issues like Russia’s war against Ukraine, saying that the conflict has reached a stalemate and “needs to be brought to a conclusion.”

Mr. Rubio was a loyal surrogate for Mr. Trump during the campaign even after being passed over as the vice-presidential pick.

A spokesman for Mr. Rubio declined to comment, and a spokesman for Mr. Trump did not immediately respond to a request for comment.

Mr. Trump has made his choice for a number of other national security roles. He has selected Representative Michael Waltz, Republican of Florida, to be his national security adviser, and Representative Elise Stefanik, Republican of New York, to be ambassador to the United Nations.

This is a developing story. Check back for updates.