Former Trump advisor Steve Bannon has agreed to testify in the Capitol riot hearings, days before he was to face trial for defying a subpoena from the committee investigating the attack on Congress, US media reported Sunday.

"Mr. Bannon is willing to, and indeed prefers, to testify at your public hearing," his lawyer Robert Costello wrote in a letter to the House Select Committee on Saturday, which was initially reported by The Guardian and cited by US media.

Bannon was among dozens of people called to testify on last year's assault on the Capitol aimed at shutting down Congress over former president Donald Trump's baseless claims that Joe Biden won the 2020 election due to voter fraud.

Investigators believe Bannon and other Trump advisors could have information on links between the White House and the mob that invaded the Capitol on the day it was due to certify Biden as winner.

Although he was not a White House employee or official Trump aide, Bannon's attorneys had previously claimed he was protected by presidential executive privilege and did not have to cooperate with the committee.

According to the letter explaining his about-face, Bannon told the House Select Committee that "circumstances have now changed."

Former Trump advisor Steve Bannon had previously refused to testify before the committee investigating the Capitol riot
Former Trump advisor Steve Bannon had previously refused to testify before the committee investigating the Capitol riot GETTY IMAGES NORTH AMERICA via AFP / Kevin Dietsch

"President Trump has decided that it would be in the best interests of the American people to waive executive privilege for Stephen K. Bannon, to allow Mr. Bannon to comply with the subpoena issued by your Committee."

In November last year, Bannon turned himself in to the FBI to face charges of contempt of Congress after refusing to testify on the January 6 Capitol assault.

"I'm never going to back down," he told reporters at the time after appearing before a judge to hear the charges.

"We're going on the offense on this. And stand by," he said, repeating the phrase Trump used during the election in 2020 to encourage supporters of a far-right militia group.

Bannon, 68, was indicted by a grand jury with two misdemeanor counts of contempt, each one carrying a penalty of one month to one year in jail, and a fine of up to $100,000.

The attack, which left five people dead, succeeded in delaying the joint House-Senate election certification session for several hours.