Gleeson spent five years with the Dons before signing at St Andrews in 2014 and his superbly-taken goal set the Blues on their way in what was an accomplished away performance.
In addition to being clinical when their chances came, the visitors were miserly in their own half with their defence ensuring that goalkeeper Tomasz Kuszczak was rarely called into action.
Kick-off was delayed for almost 10 minutes after referee Gavin Ward picked up an injury in his warm-up with assistant Robert Atkin taking charge in his place.
The match began slowly with the only real effort of note in the first 20 minutes coming when Birmingham’s David Cotterill curled a shot wide from the corner of the box.
MK Dons first opening came after 25 minutes when Rob Hall sent an effort from the edge of the area not far wide with Kuszczak rooted to the spot.
The hosts then suffered an injury blow 10 minutes before half-time when Jordan Spence was forced off with a muscle strain and he was replaced by Lee Hodson.
The best chance of a flat first half came just before the break when Samir Carruthers went through after being set up by Hall only for the former Aston Villa man to shoot into the side netting.
The Dons began the second half well with Sam Gallagher heading a half-chance wide from captain Dean Lewington’s deep cross five minutes after the restart.
But Birmingham were to open the scoring in the 57th minute when Clayton Donaldson cut the ball back for Gleeson, whose first-time effort drifted over David Martin and into the far corner.
It was the second league game in a row in which Gleeson had struck after the Irishman had gone over a year without scoring after signing for the Blues.
The hosts responded by bringing on Carl Baker and Josh Murphy, their two goalscorers from their Capital One Cup win over Cardiff on Tuesday but they were struggling to create anything of note.
Gleeson’s afternoon unfortunately ended on a sour note as he was stretchered off but his side’s lead was hardly being threatened as MK Dons continued to huff and puff.
The Blues wrapped up the game with 11 minutes left when Donaldson threaded the ball through for substitute Jacques Maghoma, who calmly rolled his shot into the bottom corner.
Hall lashed a long-range effort over for MK Dons with time ticking away but this was an afternoon of frustration for them going into the international break.