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.