Miller was a senior adviser for policy during the Trump administration and a central figure in many of the Republican's decisions. He had resisted previous efforts by the committee, filing a lawsuit last month seeking to quash a subpoena for his phone records.
Miller was interviewed virtually for about eight hours, according to a person familiar with the matter who spoke on the condition of anonymity to discuss private testimony. A second person also confirmed that Miller appeared before the committee. A spokesperson for the committee said the panel had no comment, and Miller did not immediately return a message seeking comment.
Miller is the latest in a series of sit-downs the committee has scored with those in Trump's inner circle as lawmakers move closer to the former president by questioning people who were with him on the day of the attack or were his confidants in the weeks leading up to it.
His appearance comes weeks after Ivanka Trump and her husband, Jared Kushner, also agreed to sit down with congressional investigators, months after the committee had first reached out.
Members of the panel said Kushner's testimony in late March, which lasted more than six hours, was helpful. Ivanka Trump, who was with her father in the White House on Jan. 6, was questioned for eight hours last week as congressional investigators tried to piece together her father's failed effort to delay the certification of the 2020 election results.
The nine-member panel subpoenaed the former Trump adviser in November along with Steve Bannon and former press secretary Kayleigh McEnany. Rep. Bennie Thompson, D-Miss., the panel's chairman, said at the time that Miller was aware of and had participated in "efforts to spread false information about alleged voter fraud" and had encouraged state legislatures to alter the outcome of the 2020 election by appointing alternate electors.
Thompson has also said that Miller helped prepare Trump's remarks for a rally on the Ellipse that preceded the insurrection and was with Trump when he spoke.
The House voted last week to hold former Trump advisers Peter Navarro and Dan Scavino in contempt for their monthlong refusal to comply with subpoenas. The move was the third time the panel has referred people in the former president's orbit to the Justice Department for potential prosecution for contempt. The first two referrals, sent late last year, were for former White House chief of staff Mark Meadows and Bannon.
The contempt referral against Bannon resulted in an indictment, with a trial set to start in July. The Justice Department has been slower to decide whether to prosecute Meadows, much to the committee's frustration.
By agreeing to cooperate, Miller appears to be looking to avoid the fate of those former advisers and administration officials.
For the committee, comprised of seven Democrats and two Republicans, the central facts of the insurrection are known, but what members are hoping to do with the more than 850 interviews and over 100,000 documents is fill in the remaining gaps about the attack on the Capitol. Lawmakers say they are committed to presenting a full accounting to ensure it never happens again.
The panel is examining every aspect of the riot, including what Trump was doing while it unfolded and any connections between the White House and the Trump supporters who broke into the Capitol building.
Members plan to release information in the coming months as the committee begins to hold public hearings and eventually release a series of reports on the insurrection. While there have been discussions about the possibility of eventually pursuing a criminal referral against Trump, lawmakers have not made a final decision.
Associated Press writer Nomaan Merchant in Washington contributed to this report.