Doyle nodded home a Stephen Hunt free-kick in the 66th minute to regain the lead for Reading before Kalifa Cisse set the seal on their fifth straight win which saw them leapfrog over Birmingham.
Noel Hunt had given Steve Coppell's side a 13th minute lead with a smartly taken free kick before - moments after the Irishman had suffered a blow to the head that would later see him forced to be withdrawn.
Birmingham, who have now suffered back-to-back defeats, struggled to get into the game before Kevin Phillips dragged them level with his 11th goal of the season in the 60th minute.
But they ultimately paid the penalty for not keeping Doyle in check as Alex McLeish's side slipped to their third home defeat of the season.
Birmingham were left to rue a rash challenge from James McFadden that led to Reading taking the lead.
McFadden lunged in on Noel Hunt some 20 yards from goal and referee Mike Dean had no hesitation in awarding a free-kick.
Noel Hunt then whistled a low drive past the Birmingham wall and the outstretched right hand of goalkeeper Maik Taylor.
Reading looked by far the more clinical of the two sides and Birmingham, who only threatened once in the opening period when Cameron Jerome shot wide, were lucky to get to half-time without suffering further damage.
A teasing cross from James Henry seconds after Noel Hunt struck was just asking to be converted, before Doyle stung Taylor's fingertips with a fierce close range volley in the 21st minute.
Failure to turn that first-half pressure into a decisive lead looked set to cost Reading when Birmingham skipper Lee Carsley dispossessed Cisse in the heart of midfield.
Phillips latched on to the ball, side-stepped a challenge from Ivar Ingimarsson and surged forward before beating Adam Federici from 20 yards.
Unfortunately for Birmingham, it was a false dawn as they were only on level terms for four minutes before Doyle struck.
Reading, who had to survive a scare when Phillips saw his drive tipped away by Federici, then sealed the success when Doyle turned provider in the 82nd minute with a right-wing cross that Cisse headed home at the far post for his fifth goal of the campaign.