Skipper Carlos Edwards put the hosts on their way with a stunning 25-yard strike early on before centre-back Luke Chambers, Players' Player of the Year for Town, headed home a second in the 17th minute.
Frank Nouble saw two goals chalked off for offside during a dominant first-half display from the Tractor Boys, who made sure of all three points after the break courtesy of Daryl Murphy's finish.
The Suffolk club headed into the final two games of the season six points clear of the drop zone and all but mathematically safe amid an absorbing relegation battle, and they now find themselves in the top half of the Championship table.
After loud appeals for handball were waved away, Jack Butland was forced into a brilliant save to tip over Murphy's header from Jay Tabb's corner.
But the England goalkeeper, on loan at Blues from Stoke, could only watch as Edwards' stunning long-range strike found the top corner from the right channel after just six minutes
Nikola Zigic saw his header ruled out for offside but it was the hosts who had made the better start, and it was soon 2-0.
Aaron Cresswell sent over an inch-perfect free-kick from the left wing and Chambers rose to head home from close range.
Nouble saw a third ruled out for offside before the encounter dipped into a quieter spell, with the Town striker lifting proceedings with a shot narrowly off target in the 40th minute.
It sparked a glowing finish to an impressive first-half performance from Town, who played some impressive football in the final third and, again, saw Nouble denied by the offside flag.
And all hopes of a fightback were extinguished in the 57th minute when Murphy turned and fired home from the edge of the penalty area.
It was a third goal of the game for the bluntest attack in the second tier, boasting just 45 goals from 44 games before kick-off.
And it was one which ended the game as a contest, and sparked a dip in the excitement on offer, with sub Chris Burke converting Shane Ferguson's injury-time cross to net a late consolation for Birmingham.