Per Bobby Clay of Sporting News, Tillman has graduated from the FBI's training academy and become an official agent.
Brad Biggs of the Chicago Tribune reported last September that Tillman had started training to join the FBI, whose guidelines mandate that "prospective candidates for hiring as a special agent must be at least 23 years old but younger than 37 at the time of appointment."
Tillman turned 37 on Friday.
Per Clay, a source said the two-time Pro Bowler was "currently working for the FBI. [He] has his badge and everything."
Former United States marshal Kim Widup told Clay there wouldn't be an announcement from the FBI that Tillman has become an agent in order to "get him to fade to anonymity as much as they can."
Tillman played 13 seasons in the NFL from 2003 to 2015 with the Chicago Bears and Carolina Panthers. He had 38 interceptions in 168 career games and was named the Walter Payton NFL Man of the Year in 2013.