The home side's first-half dominance was rewarded in added time when the January acquisition from Sunderland clipped Tommy Smith's clever through ball past former Bluebird Tom Heaton.
And 12 minutes into the second half the full debutant scored his third for the club, more than he managed in the whole of last season for Sunderland, after a mammoth long throw from Aron Gunnarsson.
A bizarre own goal from Ben Nugent reduced the deficit in added time but it was too little too late for the struggling Robins.
Craig Noone, back in the Cardiff side for the first time in a month, was the architect of the first chance, but Mark Hudson looked surprised to see his cross fall into his path and could only tap it into the arms of Heaton.
Five minutes later it was Noone's turn to threaten but Heaton kept out his driven left-footed effort at his near post.
Bristol City, backed by 2,200 vocal travelling fans, had a chance of their own in the 18th minute when Steven Davies' clipped cross found Jon Stead and his volley flew over the crossbar.
But that chance was a rare respite for for the visitors as Cardiff, who had failed to score more than once in a match since Boxing Day, continued to threaten down the flanks.
After Heaton did well to smother Craig Bellamy's low cross the keeper was just a spectator as Bellamy fired in a thumping 30-yard free-kick that clipped the bar.
Heaton then received the congratulations of his team-mates for a fine stop to push away a Campbell drive.
On his return to the Cardiff City Stadium Heaton was certainly being kept busy. Seven minutes before the break he had to race out of his goal to nod Noone's lofted pass out of the path of Bellamy before showing good hands to hold Peter Whittingham's effort.
And just when it looked like Sean O'Driscoll's organised Robins would make it to the break level Campbell struck. Tommy Smith's threaded pass found him inside the box and he made no mistake with a right-footed finish across goal.
Campbell was then right at the heart of the first talking point of the second half, claiming a handball by Liam Fontaine after the pair stretched to reach a Noone cross.
David Marshall had been a virtual spectator during the opening 52 minutes but he did have a worried glance over his shoulder when Liam Kelly's ambitious volley from 35 yards dropped onto the roof of his net.
Five minutes later Campbell, who scored just twice in 18 games for the Black Cats last season, grabbed his second, sending Heaton the wrong way after Gunnarsson hurled the ball into his path.
The visitors, yet to win a point on the road since O'Driscoll's appointment, then tested Marshall for the first time with 15 minutes left but the Scotland keeper pushed away Davies' fierce effort.
They did grab a consolation in added time when, under no pressure, Nugent nodded the ball past his own keeper but this is a fixture that seems increasingly unlikely to take place in next season's npower Championship.