The Terriers twice led with two goals from striker Benik Afobe, but were pegged back with Ashley Barnes and substitute Matt Sparrow replying for the League One champions.
Ward gave Lee Clark's men their fifth successive away league win with an unstoppable low shot following Afobe's pass.
Huddersfield midfielder Scott Arfield had a first-time shot saved by Peter Brezoban before striker Afobe, on-loan from Arsenal, fired Huddersfield ahead after only eight minutes.
Brighton striker Chris Wood, on-loan from West Brom, almost brought the Seagulls level by heading against the crossbar, but the home side equalised two minutes after the break when Barnes hit his 19th goal of the season from his rebounded penalty after Elliott Bennett had been brought down by Kevin Kilbane.
Afobe struck again to restore Huddersfield's lead in the 61st minute by cashing in on a defensive gaffe by Inigo Calderon, who left goalkeeper Brezovan stranded by chesting the ball down inside the area and the visitors' late pressure - defender Jamie McCombe twice forced excellent saves from Brezovan - was rewarded with Ward's late winner.