Sidney K. Powell, a member of Donald J. Trump’s legal team after he lost the 2020 election, pleaded guilty on Thursday morning to six misdemeanor counts instead of facing a criminal trial that was to begin next week. She was among 19 defendants, including Mr. Trump, who were indicted in August for their efforts to subvert the election results in Georgia.
The guilty plea was a blow to Mr. Trump, who faces the most charges of any defendant along with Rudolph W. Giuliani, his former personal lawyer. Both men face 13 counts. Significantly, it means that a member of the Trump legal team will cooperate with the prosecution as it pursues criminal convictions related to efforts to keep the former president in power after he lost the 2020 election.
Ms. Powell, 68, who appeared in a downtown Atlanta courtroom, was sentenced to six years of probation for conspiracy to commit intentional interference with performance of election duties. That is a significantly less-severe outcome than she would have faced if found guilty of the charges for which she was originally indicted, which included a violation of the state racketeering law.
She was also fined $6,000 and agreed to pay $2,700 in restitution to the state of Georgia, as well as write an apology letter to its citizens. The charges against her largely relate to her role in carrying out a breach of voting equipment in a rural Georgia county in January 2021, as Trump allies fruitlessly sought evidence of ballot fraud.
Daysha D. Young, an assistant district attorney in Fulton County, said in court that Ms. Powell had given prosecutors a recorded statement on Wednesday as part of her plea deal. She has agreed to testify against any of the 17 remaining defendants and to turn over documents in her possession related to the case.
Ms. Powell is the second to take a plea deal, a major victory for Fani T. Willis, the district attorney of Fulton County, whose team has been negotiating with some of the defendants. Last month, Scott Hall, 59, a Georgia bail bondsman, pleaded guilty to five misdemeanors. He had been accused, with Ms. Powell and others, of breaching voting equipment in Coffee County, Ga.
Few defenders of Mr. Trump promoted election fraud theories after his 2020 defeat to Joseph R. Biden Jr. as stridently as Ms. Powell. In high-profile appearances, often alongside other members of the Trump legal team, she pushed conspiracies involving Venezuela, Cuba and China, as well as George Soros, Hugo Chávez and the Clintons; she also baselessly claimed that voting machines had flipped millions of votes from Mr. Trump to Mr. Biden.
But on Thursday, she herself pleaded guilty to taking part in a conspiracy to tamper with an election. During Ms. Powell’s appearance in Fulton County Superior Court on Thursday morning, Judge Scott McAfee asked her: “Are you pleading guilty today because you agree that there is a sufficient factual basis, that there are enough facts, that support this plea of guilty?”
“I do,” she replied.
Ms. Powell was prosecuted under the Georgia First Offender Act, which allows people with no prior felonies to avoid having the conviction on their permanent record if they comply with the terms of their sentence. Ms. Young, the prosecutor, noted in court that if Ms. Powell successfully complies with her sentence, she can then “honestly say” that she has “never been convicted of these charges.”
Ms. Powell’s lawyer, Brian T. Rafferty, filed numerous motions ahead of the trial seeking to have the charges dismissed, but they were denied by the judge. Before her plea agreement, Mr. Rafferty even claimed in filings that Ms. Powell “did not represent President Trump or the Trump campaign” after the election.
But those claims were undercut by Ms. Powell’s own past words, as well as those of Mr. Trump and ample video evidence of her taking part in news conferences alongside other members of the Trump legal team. Mr. Trump once even specifically referred to Ms. Powell as a member of his “truly great team.”
It was not immediately clear what impact the plea would have on Ms. Powell’s law license. A spokeswoman for the Texas Bar Association said it would not affect a disciplinary proceeding already underway, and was not sure if it would result in a separate disciplinary case. The current case, which concerns misrepresentations she is accused of having made in lawsuits filed after the 2020 election, was dismissed by a lower court but has been appealed by the bar association.
Ms. Powell was a frequent visitor to the White House after the election and had direct dealings with the highest-profile defendants in the case, including Mr. Trump, who considered naming her a special counsel to review vote fraud. That makes her potentially a valuable witness for the prosecution.
“I think it’s very bad news for Trump,” said Clark D. Cunningham, a law professor at Georgia State University, noting that her access to Mr. Trump at the White House put her “right in the middle” of the racketeering conspiracy at the heart of the case.
Most of the charges against Ms. Powell involved the data breach at the Coffee County elections office. There, on the day after the Jan. 6 riot, Trump allies copied sensitive and proprietary software used in voting machines throughout the state to hunt for ballot fraud. Ms. Powell was not there, but she was one of the lawyers who hired a consulting firm, SullivanStrickler, that assisted in the effort. The firm invoiced Ms. Powell more than $26,000 for its work, and her organization, Defending the Republic, paid the bill.
Brad Raffensperger, Georgia’s secretary of state, subsequently replaced Coffee County’s voting machines and said that “the unauthorized access to the equipment” had violated Georgia law. Ms. Powell’s restitution will go toward covering the costs of replacing the election equipment, prosecutors said.