Former Wolves boss McCarthy only took the reins at Town on Thursday morning but his impact has been instant, with the Suffolk outfit claiming only their second league win of the season and first since late August, although they still remain rooted to the foot of the npower Championship.
It was an immediate return to the West Midlands for the Yorkshireman, whose six-year stint at Wolves was brought to an end in February, but it was a former Blues striker who did the damage.
DJ Campbell, who enjoyed 18 months at St Andrew's, turned and struck home his third goal in five appearances since joining on loan from QPR to secure the decisive matchwinner after just eight minutes.
Blues, who gave the ball away far too often, lacked spark throughout as they struggled to replicate their away form on home soil, with this now four home matches without a win for Lee Clark's side, who were booed off the pitch.
It could and should have been a point apiece but substitute Nikola Zigic wasted two golden second-half chances.
McCarthy, who replaced Paul Jewell, opted for experience over youth in his first game in charge, recalling former Blues midfielder Guirane N'Daw from the cold along with fellow midfielder Nigel Reo-Coker in favour of Luke Hyam and Josh Carson.
And after a distinctly ordinary opening to proceedings it was Ipswich who drew first blood with just eight minutes on the clock.
Nathan Redmond gave possession away cheaply in the middle of the park and Lee Martin's effort fell to Campbell, who turned and dispatched a fine shot across Jack Butland.
Blues, unchanged for a third successive match, were not at the races in the opening 20 minutes or so although Wade Elliott brought a save out of Ipswich keeper Stephen Henderson.
Daryl Murphy tested Butland with a low effort before Marlon King forced Henderson to tip over his goalbound 25-yard free-kick at the other end.
Martin was next to try his luck from distance with a shot which Butland turned behind before the first half fizzled out, with Blues booed off at the break.
Clark turned to Chris Burke in an attempt to inspire his side but it had little immediate effect.
Danny Higginbotham's header brought a good save from Butland after Blues had switched off from Ipswich's short set-piece.
King then saw his penalty appeals rejected before Clark rolled the dice again, this time turning to Zigic.
Elliott blasted wide for the home side when well placed before Zigic, in space, somehow headed wide from King's inch-perfect cross when he really should have scored.
The towering Serbian striker wasted another great opportunity moments later when he fired straight at Henderson when clean through.
Ravel Morrison's deft chip found the roof of the net before Curtis Davies blasted over in injury time as Blues continued to push for an equaliser, but Ipswich held firm to claim their first three points at St Andrew's since 1986.
Source: PA