The Lions went into the encounter as the second tier's form side having won four of their last five, boasting four successive clean sheets in the process.
And they should have taken the lead as they enjoyed the better of the opening half-hour, Chris Wood heading a great chance over while Town goalkeeper Stephen Henderson denied Andy Keogh, Liam Trotter and James Henry.
Campbell punished the visitors as he then converted a flowing move from close range for his seventh goal in 12 games since joining on loan from QPR.
The striker turned provider five minutes after half-time as he chased down Danny Shittu, gained possession and fed Daryl Murphy to sweep home.
Campbell then bagged his second from the penalty spot after Shane Lowry's handball - Town's fourth successive game in which they have been awarded a spot-kick.
Campbell's form will certainly give QPR boss Harry Redknapp food for thought, with his loan stay due to expire in January.
It is the first time Ipswich have recorded three successive wins in 10 months while Mick McCarthy has now won five of his eight games since taking charge.