WASHINGTON — The former White House counsel, Pasquale “Pat” Cipollone met for a private interview with the January 6 committee for about eight hours Friday regarding his role in trying to prevent President Trump from challenging the 2020 presidential election and joining the violent mob that laid siege to the Capitol.

Mr. Cipollone, once a staunch presidential confidant who had defended Trump during his first impeachment trial, had been reluctant to appear formally for an on-record interview. Like other former White House officials, it is possible he claimed his counsel to the Republican president as privileged information he was unwilling to share with the committee.

It remained unclear after he left the Capitol Hill building Friday afternoon whether he had remained within those parameters during the hours-long interview.

Mr. Cipollone has been a sought-after witness after bombshell testimony revealed his apparently desperate and last-ditch efforts to prevent Mr. Trump’s actions. 

The panel was told he warned the defeated president would be charged with “every crime imaginable” if he went to the Capitol on January 6, 2021, trying to stop the certification of President Biden’s election. Mr. Cipollone was subpoenaed for his testimony.

The panel said Mr. Cipollone is “uniquely positioned to testify” in a letter accompanying the subpoena issued last week.

“Mr. Cipollone repeatedly raised legal and other concerns about President Trump’s activities on January 6th and in the days that preceded,” the committee’s chairman, Representative Bennie Thompson, said in a statement. 

“While the Select Committee appreciates Mr. Cipollone’s earlier informal engagement with our investigation, the committee needs to hear from him on the record, as other former White House counsels have done in other congressional investigations.”

Mr. Cipollone’s central role came into focus during a surprise committee hearing last week when a former White House aide, Cassidy Hutchinson, described his repeated efforts to stop Mr. Trump from joining the mob at the Capitol.

Ms. Hutchinson said Mr. Cipollone urged her to persuade her boss, the chief of staff, Mark Meadows, not to let Mr. Trump go to the Capitol.

Ms. Hutchinson testified that she was told Mr. Trump was irate when he was ultimately prevented by his security team from going to the Capitol that day. The Secret Service has disputed parts of her account detailing Mr. Trump’s actions when she said he lashed out at the driver in the presidential motorcade.

Mr. Cipollone was also part of a key meeting on the Sunday before the January 6 attack with Justice Department officials at the White House threatening to resign if Mr. Trump went ahead with plans to install a new acting attorney general who would pursue his false claims of voter fraud.

One witness testified to the committee that during that meeting Mr. Cipollone referred to a proposed letter making false claims about voter fraud as a “murder-suicide pact.”

Mr. Cipollone and his lawyer, Michael Purpura, who also worked at the Trump White House, did not respond to requests for comment.

Earlier this week, Mr. Trump responded to news of Mr. Cipollone’s cooperation on his social media platform, Truth Social, calling it bad for the country.

“Why would a future President of the United States want to have candid and important conversations with his White House Counsel if he thought there was even a small chance that this person, essentially acting as a ‘lawyer’ for the Country, may someday be brought before a partisan and openly hostile Committee in Congress,” the former president said.