[7] He made his NFL debut during the league season opener on September 6, 2018, against the Atlanta Falcons, playing on special teams.

[8] Maddox recorded his first career interception by picking off a pass from Tennessee Titans' quarterback Marcus Mariota in a 26–23 overtime loss on September 30.

On September 26, 2019, late in a game against the Green Bay Packers, Maddox collided helmets with teammate Andrew Sendejo on an attempted tackle of Jamaal Williams and had to be carted off the field on a stretcher.

The Eagles announced that Maddox had movement in all of his extremities, but was taken to a local hospital overnight as a precaution and for further evaluation; he returned with the team the next day.

On December 18, 2020, Maddox was placed on season-ending injured reserve after suffering a knee injury in a Week 14 win over the New Orleans Saints.

[19] Maddox reached Super Bowl LVII where the Eagles lost 38–35 to the Kansas City Chiefs; he recorded seven tackles in the game.