Former national security advisor Mike Flynn has hired attorney Sidney Powell as his new counsel, Hill.TV has learned.

"I'm honored to be representing General Flynn, who I've long considered an American hero. The General and his family want to thank everyone across the country for their cards and contributions to his legal defense fund. He is going to continue to cooperate with the government, pursuant to his plea agreement," Powell told Hill.TV in a phone call.

Powell is author of the new book "Licensed to Lie, Exposing Corruption in the Department of Justice." The book's description reads, "Licensed to Lie reveals the strong-arm, illegal, and unethical tactics used by headline-grabbing federal prosecutors in their narcissistic pursuit of power to the highest halls of our government" and focuses on the conduct of the Justice Department during the Enron investigation in the mid-2000s.

Powell is a frequent presence on the Fox News and prominent critic of Mueller's investigation.

Flynn terminated Covington & Burling LLP as his counsel last week. The former national security advisor plead guilty last year to lying to the FBI and agreed to cooperate with Mueller's investigation. Flynn's sentencing has been delayed on several occasions.