Donald Trump’s former attorney Rudy Giuliani is expected to cooperate with the House select committee investigating January 6, and potentially reveal his contacts with Republican members of Congress involved in the former president’s effort to overturn the results of the 2020 election.

The move by Giuliani to appear before the panel – in a cooperation deal that could be agreed within weeks, according to two sources briefed on negotiations – could mark a breakthrough moment for the inquiry as it seeks to interview key members of Trump’s inner circle.

That is the case because even though Trump’s allies and Republican members of Congress already known to have been involved in such efforts have refused to help the panel, Giuliani is now in a position to inform House investigators about any possible culpability.

Broadly, Giuliani has indicated through his lawyer to the select committee that he will produce documents and answer questions about Trump’s schemes to return himself to office on 6 January that House investigators had outlined in a subpoena issued to him last month.

The former president’s attorney is prepared to reveal his contacts and the roles played by Republican members of Congress in the scheme Giuliani helped orchestrate to have then-vice-president Mike Pence stop the certification of Joe Biden’s election victory.

Giuliani is also prepared to divulge details about Trump’s pressure campaign on Pence to adopt the scheme, and the effort coordinated by him and the Trump White House to have legislatures certify slates of electors for Trump in states actually won by Biden.

But the former president’s attorney has indicated that he will assist the select committee only if his appearance is not pursuant to his subpoena, and does not have to give records or discuss his contacts with Trump over executive and attorney-client privilege concerns.

Giuliani is prepared to make exceptions in instances where the panel can demonstrate that meetings with Trump that would have otherwise been subject to those protections might have been broken, and that the protections should not apply.

The demands surrounding the circumstances of his cooperation reflect comments he made on Newsmax last week when he falsely claimed the select committee was “illegal”, and claimed that “it doesn’t have minority membership and really can’t subpoena anybody.”

The select committee appears to have ignored his remarks as they move to finalize an agreement with Giuliani. The comments did not come up in recent talks and the panel last week allowed Giuliani to postpone his document production deadline for a second time, one of the sources said.

That may be explained in large part because of the panel’s determination to get the cooperation of one of Trump’s closest if problematic advisers who was involved in efforts to overturn the 2020 election from the start – and has a penchant for sometimes revealing too much.

Giuliani could speak to events such as a 18 December 2020 meeting in the Oval Office where Trump reviewed a draft executive order to seize voting machines and verbally agreed to install conspiracy theorist Sidney Powell as special counsel to investigate election fraud.

The Guardian has reported that Giuliani then led the Trump “war room” at the Willard hotel in Washington DC when Trump called from the White House and discussed ways to stop Biden’s certification – and could speak to non-privileged elements of the plan.

The cooperation deal would also technically involve Giuliani turning over documents in addition to appearing before the select committee, the sources said, but the logistics were unclear given the FBI last year seized his devices that he used on 6 January.

Giuliani is committed to appearing before the panel, the source said, but it was not clear whether he would testify under oath in a closed-door deposition, for which the select committee has been pushing, or appear in a more informal interview on Capitol Hill.

A spokesperson for the select committee declined to comment on negotiations with witnesses. The sources added negotiations could still collapse, but if a deal could be agreed, Giuliani would probably appear before the panel at least before the end of March.

The select committee has been quietly making substantial progress in its investigation into the events of 6 January, securing records from the National Archives, as well as documents and testimony from some of Trump’s top aides and advisers.

Last month, the chairman of the panel, congressman Bennie Thompson, revealed that House investigators had spoken to more than 500 witnesses and obtained more than 50,000 documents, including thousands from Trump’s former White House chief of staff, Mark Meadows.

The willingness by Giuliani to negotiate what appears to be an expansive cooperation deal has come in stark contrast to the defiance expressed by the initial set of Trump aides and advisers who were subpoenaed by the select committee last year.

Trump’s former chief strategist Steve Bannon refused to comply with his subpoena in its entirety, boasting executive privilege protection – only to be referred to the justice department for criminal contempt of Congress and indicted on two counts about four weeks later.

That has served as a warning to other witnesses. Even if his cooperation deal ultimately falls through, Giuliani may be engaging with the select committee at least to avoid a similar fate to Bannon and a potentially costly legal battle to fight such charges.

The benefits of partial cooperation have also become apparent, after Meadows was held in contempt of Congress for refusing to appear for a deposition as required by his subpoena, but remains unindicted two months after his initial referral to the justice department.