Hughes will link up with former Dragons defence coach Simon Cross, who is the head coach at Old Glory DC.
Hughes has thanked Dragons for granting him an early release after he spoke to head coach Dai Flanagan.
“They have been fantastic and very supportive in allowing me to pursue an opportunity that is once in a lifetime,” said Hughes.
“I’ll leave the club with many fond memories.”
Hughes’ departure means Dragons will have Harry Wilson, Aneurin Owen, Joe Westwood and Harri Ackerman competing for the centre spots.
“Steff has been a fantastic servant throughout his time with us and leaves with our best wishes for the future,” said Flanagan.
“I’ve been fortunate to work with Steff for more than a decade, with our time at Scarlets and now Dragons, and I have the utmost respect for the way he always conducts himself and plays the game.
“Steff is an excellent professional, a leader, and he leaves a legacy.
“He has helped bring on the likes of Aneurin Owen and Joe Westwood and raised the bar with the way our squad operates off the field.”
