Steve Bannon, Donald Trump’s former presidential adviser, has been convicted of contempt of Congress for defying a subpoena from the committee investigating last year’s attack on the US Capitol.

A jury found Bannon, 68, guilty of two misdemeanour counts for refusing to provide testimony or documents to the House of Representatives select committee as it scrutinises the January 6, 2021 rampage by Trump supporters who tried to upend the results of the 2020 presidential election.

Each contempt of Congress count is punishable by 30 days to one year behind bars, as well as a fine of $US100 to $US100,000 ($145 to $144,745).

US District Judge Carl Nichols set a sentencing date of October 21.

The verdict by the jury of eight men and four women, after less than three hours of deliberations, marked the first successful prosecution for contempt of Congress since 1974, when a judge found G Gordon Liddy, a conspirator in the Watergate scandal that prompted president Richard Nixon’s resignation, guilty.

The guilty verdict comes after the committee heard Mr Trump ignored pleas from his children and other close advisers to urge his supporters to stop the violence.

Witnesses told the congressional hearing Mr Trump watched the deadly attack on the US Capitol unfold for hours, but did nothing.

Former White House senior strategist Steve Bannon leaves the Federal District Court House after the guilty verdict. Photo: Getty

Mr Bannon was a key adviser to the Republican Trump’s 2016 presidential campaign, then served as his chief White House strategist during 2017 before a falling out between the two that was later patched up.

“We may have lost the battle here today; we’re not going to lose this war,” Mr Bannon told reporters after the verdict.

Mr Bannon castigated the “members of that show-trial committee” who he said “didn’t have the guts to come down here and testify in open court”.

Mr Bannon elected not to testify in his own defence.

His defense team in closing arguments on Friday suggested to jurors that Mr Bannon was a political target and painted the main prosecution witness as a politically motivated Democrat with ties to one of the prosecutors, including belonging to the same book club.

The prosecution said Mr Bannon showed disdain for the authority of Congress and needed to be held accountable for unlawful defiance.

Prosecutor Molly Gaston told jurors the attack represented a “dark day” for the US, adding: “There is nothing political about finding out why January 6 happened and making sure it never happens again.”

Evan Corcoran, one of Mr Bannon’s lawyers, told jurors, “The question is, ‘Why? Why was Steve Bannon singled out?”

The trial featured two days of testimony.

Prosecutors questioned only two witnesses.

The defence called none.

Steve Bannon’s lawyer Evan Corcoran arrives for the trial. Photo: Getty

The conviction may strengthen the committee’s position as it seeks to secure testimony and documents from others in Mr Trump’s orbit.

Mr Trump last year asked his associates not to cooperate with the committee, accusing it of trying to hurt him politically, and several of them rebuffed the panel.

Another former Trump adviser, Peter Navarro, was separately was charged with contempt of Congress in June for refusing to appear for a committee deposition.

Mr Navarro’s trial is scheduled for November.

The Justice Department opted not to charge two other Trump associates, Mark Meadows and Daniel Scavino, for defying the committee despite a House vote recommending it.

Unlike Mr Bannon, Mr Meadows turned over some communications to the committee.

The committee could make multiple referrals to the Justice Department seeking criminal charges against Trump himself, according to its vice chair Liz Cheney.

The main prosecution witness was Kristin Amerling, a top committee staffer who testified that Mr Bannon spurned deadlines to respond to the September 2021 subpoena, sought no extensions and offered an invalid rationale for his defiance — a claim by Trump involving a legal doctrine called executive privilege that can keep certain presidential communications confidential.

The Justice Department charged Mr Bannon last November after the Democratic-led House voted the prior month to hold him in contempt.

A pro-Trump mob stormed the Capitol and attacked police with batons, sledgehammers, flag poles, Taser devices, chemical irritants, metal pipes, rocks, metal guard rails and other weapons in a failed effort to block congressional certification of his 2020 election loss to Democrat Joe Biden.

The committee has said Mr Bannon spoke with Mr Trump at least twice on the day before the attack and attended a planning meeting at a Washington DC hotel.

It played a clip of Mr Bannon saying on his podcast the day before the attack that “all hell is going to break loose tomorrow”.

The judge limited the scope of the case Mr Bannon’s team could present to jurors, moves one of his lawyers said “badly stymied” the defence.

Mr Bannon was barred from arguing that he believed his communications with Mr Trump were subject to executive privilege and was prohibited from arguing he relied on legal advice from a lawyer in refusing to comply.

Mr Bannon’s defence argued that he believed the subpoena deadlines were flexible and subject to negotiation between his lawyer and the committee.

In an 11th-hour reversal with the trial looming, Mr Bannon this month announced a willingness to testify in a public hearing before the committee, an offer that prosecutors said did not change the fact he had already broken the law.