The Justice Department decided not to charge Paula Broadwell. Petraeus resigned as CIA director in November after he admitted to an affair with Broadwell.
The affair was exposed during an FBI investigation of Broadwell's emails to a romantic rival, Jill Kelley.
Those emails allegedly warned Kelley to stay away from Petraeus and General John Allen, the U.S. commander in Afghanistan.
A spokesman for Broadwell says she and her family are "pleased with this decision and pleased that this is resolved." Broadwell does not appear to be the subject of any other Justice Department investigations.
The Associated Press contributed to this report.