Another former lawyer for Donald Trump, Jenna Ellis, pleaded guilty on Tuesday to helping the former US president's efforts to overturn his 2020 election defeat in the state of Georgia and agreed to testify against Trump if called upon.

Ellis is the third member of Trump's legal team to reach a plea deal since Thursday, following Sidney Powell and Kenneth Chesebro, and the fourth of the 19 people charged in the sweeping racketeering indictment brought by Fulton County District Attorney Fani Willis to agree to testify..

Ellis, her voice cracking at times, told an Atlanta court that she "failed to do my due diligence" in vetting claims about voter fraud from other Trump attorneys.

"What I did not do and should have done, your honor, was to make sure that the facts the other lawyers alleged to be true were in fact true," Ellis told Fulton County Superior Court Judge Scott McAfee. "I look back on this whole experience with deep remorse."

The case is one of four that Trump, who has pleaded not guilty, faces as he runs for president as the frontrunner for the Republican nomination in 2024, and one of two that relate to his efforts to overturn his 2020 election loss to Democrat Joe Biden.

Ellis, 38, pleaded guilty to aiding and abetting false statements and writings.

Prosecutors said she attended a meeting with Georgia lawmakers where Trump personal lawyer and former New York Mayor Rudy Giuliani made false claims about voting irregularities. The meeting was part of an unsuccessful effort to persuade lawmakers to refuse to certify Biden's narrow victory in the state, prosecutors said.

Ellis frequently appeared alongside Giuliani in the weeks after the election, members of what Ellis called "an elite strike force" to challenge the results on Trump's behalf.

The plea agreement calls for her to be sentenced to five years of probation and US$5,000 in restitution. (Reuters)