The Belgian forward will represent D.C. United under manager Wayne Rooney.
Benteke made 177 appearances and scored 37 goals during his time in south London, finishing top scorer in 2016/17.
Chairman Steve Parish said of his departure: “Christian has played a crucial role in this club’s Premier League journey, making an immediate impact after signing and playing a central role in the squad ever since.
"He’s someone I’ve enjoyed a great relationship with and he’s shown incredible loyalty staying with the club when he could easily have taken other options. We all wish him all the very best with the next stage of his career.”