President Trump's former national security adviser Michael Flynn as he arrived in December at the federal court in Washington. (Carolyn Kaster/AP)

President Trump’s former national security adviser Michael Flynn has retained conservative lawyer and commentator Sidney Powell as his new counsel as he awaits sentencing for lying to the FBI about his Russian contacts in Robert S. Mueller III’s probe of interference in the 2016 election.

Powell, a former federal prosecutor and critic of Mueller’s investigation, released a statement saying, “Attorney Sidney Powell is honored to represent General Flynn, and he will continue to cooperate with the government in all matters.”

Flynn’s former defense attorneys Robert K. Kelner and Stephen P. Anthony notified a federal judge Thursday that Flynn had terminated his Covington & Burling defense team and had a new attorney.

In Powell, Flynn has chosen a white-collar defense appeals specialist and occasional Fox News commentator who has criticized Mueller and the Russia investigation and clashed previously with one of his top lieutenants in the Russian investigation, Andrew Weissmann.

Powell worked as a federal prosecutor in Texas and Virginia earlier in her career before entering private practice. She is the author of a 2014 book titled “Licensed to Lie, Exposing Corruption in the Department of Justice,” in which Weissmann was a target of criticism over alleged incidents involving a defendant Powell represented in the Justice Department’s investigation of the collapse of the Houston energy company Enron in 2001.

In a Thursday morning tweet, Trump voiced his approval of Flynn’s choice.

“General Michael Flynn, the 33 year war hero who has served with distinction, has not retained a good lawyer, he has retained a GREAT LAWYER, Sidney Powell. Best Wishes and Good Luck to them both!” the president said.

Flynn pleaded guilty in December 2017 to falsely telling the FBI in an interview that he had not discussed sanctions with then-Russian Ambassador Sergey Kislyak before Trump’s inauguration.

Flynn agreed to cooperate in Mueller’s investigation, leading to his sentencing being delayed to December 2018.

U.S. District Judge Emmet G. Sullivan postponed sentencing at that time after lambasting the former three-star general and his lawyers for suggesting the FBI had duped Flynn. “Arguably, you sold your country out,” Sullivan told Flynn at the time.

Flynn then asked that his sentencing be postponed, promising to continue cooperating with the government. A new sentencing date has not been set.

Flynn is expected to testify in Alexandria, Va., at the federal trial of his former business partner Bijan Kian in July. Kian has been charged with working as an unregistered agent of Turkey; he has pleaded not guilty.