Roberts, a £250,000 summer signing from Ipswich, was the star of the show for Town, who have not lost to Bradford in four years.
Huddersfield broke the deadlock three minutes into the second period at the Galpharm Stadium when midfielder Jon Worthington ghosted in unmarked to nod home Robbie Williams' cross.
Roberts opened his account just after the hour mark, with the winger bursting past Graeme Lee before sending Rhys Evans the wrong way.
Town left-back Williams sealed the game as a contest after 75 minutes courtesy of a delightful 25-yard free-kick, and Roberts rubbed salt into the visitors' wounds with 10 minutes left by tapping home Danny Cadamarteri's dangerous raid.
Bradford should have taken the lead after 25 minutes, but new signing Michael Boulding toe-poked his shot into the side-netting after Huddersfield goalkeeper Matt Glennon had spilled Barry Conlon's flick-on.