Broadwell's affair with former CIA Director David Petraeus came to light during the investigation into emails she sent another woman and led to his resignation.
Lawyer Robert Muse told CNN he received a letter from federal prosecutors, dated Dec. 14, and that he was "very pleased that the U.S. attorney's office in Tampa very promptly resolved this matter."
Broadwell, who co-authored a biography of Petraeus, could still be prosecuted for possession of classified material. Investigators discovered information on her computer that was described as classified but not especially sensitive.
The investigation began when Jill Kelley of Tampa, Fla., reported to the FBI that she had received anonymous emails she considered harassing. Kelley hosted parties for commanders from MacDill Air Force Base and she became close to Petraeus when he headed Central Command, and to Gen. John Allen.
Allen succeeded Petraeus as commander of NATO forces in Afghanistan. His nomination to command U.S. forces in Europe has been delayed by an investigation into whether some of his email exchanges with Kelley were "inappropriate."
Petraeus, Broadwell, Kelley and Allen are all married.