The hosts salvaged a share of the spoils in the Sky Bet Championship fixture with Demarai Gray following up his winner against Wolves last weekend with another classy piece of finishing in the 78th minute.
Blackburn captain Matt Kilgallon had put Rovers ahead after just eight minutes with his first goal in over a year.
A stirring second-half fight back from Birmingham saw them draw level when full-back Jonathan Grounds grabbed a 64th-minute equaliser.
The ever reliable Jordan Rhodes looked to have earned Blackburn only their second win in their last five Championship games with his 18th goal of the season four minutes later.
But Gray popped up to ensure Birmingham extended their unbeaten home record to seven games, while Rovers have now not been beaten in eight league and cup matches on the road.
Rovers went close early on when Craig Conway cut in from the left only to see his shot well saved by Darren Randolph.
Conway then turned provider three minutes later as his corner picked out the unmarked Kilgallon, who comfortably headed home from eight yards.
Birmingham took some time to regroup after falling behind but the lively winger David Cotterill did his best to try and find them a route back into the game.
The Wales international saw his 18th-minute drive comfortably saved by goalkeeper Simon Eastwood and two minutes later he whipped a free-kick over the bar.
While Eastwood had little trouble dealing with Cotterill’s shot he needed to be a lot more alert on the stroke of half-time as Birmingham continued their search for an equaliser.
Former Republic of Ireland international midfielder Stephen Gleeson let fly from 30 yards, forcing Eastwood to push away the deflected drive as it threatened to sneak in at his near post.
Birmingham did finally find a way past Eastwood 12 minutes into the second-half when Clayton Donaldson lifted the ball towards goal after being set-up by Gray, but a superb goal-line clearance by Ben Marshall kept the visitors’ lead intact.
That sparked a spell of intense Birmingham pressure with Robert Tesche seeing his shot blocked and Michael Morrison heading inches wide.
The Blackburn goal was leading a charmed life and their luck finally ran out when Grounds met a Cotterill corner to power a header past Eastwood at his near post.
But all the hard work that Birmingham had put in to draw level was wasted just four minutes later.
Goalkeeper Randolph came to collect a cross from Markus Olsson but let the ball slip from his grasp to present Rhodes with the simple chance of rolling the ball into an unguarded net.
Randolph did make amends for that error when he denied Marshall from close range with Conway seeing his follow-up cleared off the line.
It was a let off that City made the most off just seconds later when skipper Paul Caddis picked out Gray who calmly curled the ball beyond Eastwood from 14 yards.