Riley is joining the team on a one-year deal and will help fill the void at linebacker after the team released Kyle Van Noy earlier this offseason.
Riley, 26, has played for both the Eagles and the Atlanta Falcons in his career.
He has appeared in 57 games over four seasons and has made 24 starts.
Last season, Riley appeared in 13 games for the Eagles and recorded 55 tackles.
The Dolphins are continuing to fill out their roster on defense as they look to become a playoff team in the upcoming season.
Miami was 10-6 last season, but it missed the playoffs after losing to the Buffalo Bills in Week 17.