Federal immigration authorities on Saturday detained a well-known activist who played a major role in Columbia University’s pro-Palestinian student movement last year, his lawyer said on Sunday.

The arrest of the activist, a legal permanent resident of the United States, was a significant escalation of President Trump’s crackdown on what he has called antisemitic campus activity.

The activist, Mahmoud Khalil, is of Palestinian heritage and graduated in December with a master’s degree from the university’s school of international affairs, according to his LinkedIn. His lawyer, Amy Greer, confirmed that he was a green card holder and said the arrest would face a vigorous legal challenge.

“We will vigorously be pursuing Mahmoud’s rights in court, and will continue our efforts to right this terrible and inexcusable — and calculated — wrong committed against him,” Ms. Greer said in a statement. The arrest, she said, “follows the U.S. government’s open repression of student activism and political speech.”

Ms. Greer said she was not sure of Mr. Khalil’s “precise whereabouts,” and that he may have been transferred as far away as Louisiana. Mr. Khalil’s wife, an American citizen who is eight months pregnant, tried to visit him at a detention center in New Jersey but was told he was not being held there, Ms. Greer said.

A spokeswoman for the Department of Homeland Security, Tricia McLaughlin, said in a statement on Sunday night that Mr. Khalil had been arrested “in support of President Trump’s executive orders prohibiting antisemitism.”

“Khalil led activities aligned to Hamas, a designated terrorist organization,” she said. “ICE and the Department of State are committed to enforcing President Trump’s executive orders and to protecting U.S. national security.”

Secretary of State Marco Rubio shared a link on X to a news article about Mr. Khalil’s arrest and issued a broad promise: “We will be revoking the visas and/or green cards of Hamas supporters in America so they can be deported.”

The immigration agents who detained Mr. Khalil told him his student visa had been revoked, Ms. Greer said, even though he does not currently hold such a visa. Revoking a green card is quite rare, said Elora Mukherjee, the director of the immigrants’ rights clinic at Columbia Law School, and in a vast majority of cases where it does happen, the holder has been accused and convicted of criminal offenses, she said.

If the government was to revoke Mr. Khalil’s green card “in retaliation for his public speech, that is prohibited by the First Amendment of the U.S. Constitution,” Ms. Mukherjee said, adding that she was still learning details about this particular case.

Jodi Ziesemer, the director of the immigrant protection unit at the New York Legal Assistance Group, said the revocation process is typically lengthy. A green card holder can be detained, but not deported, during that process, she said.

Mr. Khalil was a fixture at the protests that engulfed Columbia last spring, making the Manhattan campus the national epicenter of demonstrations against the war in Gaza. He described his role to reporters as a negotiator and spokesman for Columbia’s pro-Palestinian group, Columbia University Apartheid Divest.

The Trump administration has made Columbia the first target of its push to punish what the president has deemed elite schools’ failures to protect Jewish students during campus protests.

On Friday, the administration announced that it had canceled $400 million in grants and contracts to the university. In a social media post last week, Mr. Trump vowed to punish individual protesters his administration considered “agitators.”

“All federal funding will STOP for any College, School or University that allows illegal protests,” Mr. Trump wrote. “Agitators will be imprisoned/or permanently sent back to the country from which they came. American students will be permanently expelled or, depending on the crime, arrested.”

In a statement on Sunday, Columbia administrators did not comment directly on the arrest.

“Columbia is committed to complying with all legal obligations and supporting our student body and campus community,” the statement read. “We are also committed to the legal rights of our students and urge all members of the community to be respectful of those rights.”

The arrest drew swift condemnation from some free speech groups, immigrant rights’ activists and politicians on Sunday.

Donna Lieberman, the director of the New York Civil Liberties Union, said in a statement that the detention “reeks of McCarthyism.” She added that the arrest was “a frightening escalation of Trump’s crackdown on pro-Palestine speech and an aggressive abuse of immigration law.”

Zohran Mamdani, a Queens assemblyman who is running for mayor, called the detention “a blatant assault on the First Amendment and a sign of advancing authoritarianism under Trump.” Mr. Mamdani, a democratic socialist, has faced backlash from some pro-Israel groups for his criticism of Israel.

And Murad Awawdeh, the president of the New York Immigration Coalition, said in a statement, “This blatantly unconstitutional act sends a deplorable message that freedom of speech is no longer protected in America.”

But the Columbia Jewish Alumni Association, which has been calling for aggressive action against pro-Palestinian demonstrators, praised Mr. Khalil’s detention in a series of social media posts, calling Mr. Khalil, without evidence, a “ringleader“ of the chaos at Columbia.

Mr. Khalil told Reuters before his arrest on Saturday that he feared that he would be targeted by the federal government.

“Clearly Trump is using the protesters as a scapegoat for his wider agenda fighting and attacking higher education and the Ivy League education system,” he said.

Mr. Khalil was active as a negotiator for protesters last week at Barnard College, a women’s college affiliated with Columbia, which erupted after the college announced that it was expelling two students for disrupting a course on modern Israel. When Barnard’s president, Laura Rosenbury, called protesters on the phone to negotiate during one sit-in on campus, Mr. Khalil held up a megaphone to amplify her voice.

Mr. Khalil himself was briefly suspended from Columbia last spring for his role in the protests before the school reversed the decision. He has a diplomatic background and has worked at the British Embassy in Beirut, according to an online biography.

Over the last few days, critics of the protest movement at Columbia have singled out Mr. Khalil on social media. Shai Davidai, a vocal pro-Israel professor at Columbia who was barred from campus after the university said he intimidated and harassed employees, called on Mr. Rubio to deport Mr. Khalil.

Sharon Otterman contributed reporting.