Darby, who sustained a torn ACL last November, continued his rehab while exploring his options when free agency opened. The defensive back visited the Kansas City Chiefs on Thursday before electing to remain with the Eagles.
The team hasn't announced a timetable for Darby's return, putting his status in question for the Eagles' season-opener in 2019.
The Buffalo Bills originally selected Darby in the second round of the 2015 NFL Draft. He spent two seasons with the Bills before being traded to the Eagles in 2017.
Darby has struggled to stay healthy in his two years with Philadelphia, playing only 17 total games. He made nine starts last season before suffering the ACL injury and missed half of the 2017 campaign with a dislocated ankle.
Darby has appeared in 46 career games (45 starts), recording 214 total tackles, six interceptions and 54 passes defensed.