Gerrard came on as a substitute seconds before the break and drove home a hotly disputed spot-kick in the second half to rescue a point.
Liverpool led early on through a David Ngog goal but Christian Benitez nodded the equaliser and Cameron Jerome smashed home a stunning 30-yarder to put Birmingham ahead until Gerrard's intervention.
Joe Hart had saved one Ngog effort before the France Under-21 striker gave Liverpool a 13th-minute lead. Glen Johnson surged down the right, cutting between two defenders before crossing for Ngog to see his first effort blocked by Hart.
The ball flew to Dirk Kuyt, and again Hart got his legs in the way to deflect a firm effort. But when the rebound dropped for Ngog, there was no mistake with a close-range volley into the roof of the net.
Birmingham struck back with an impressive set-piece. James McFadden fired a free-kick into the box, Roger Johnson headed back across goal where Scott Dann nodded on for Ecuador striker Benitez to head past Jose Reina from close range.
A minute from the break Albert Riera, who had been on a solo bid to score from outside the box at every opportunity, suffered a recurrence of his hamstring injury, and Gerrard was instantly sent on as substitute.
And within seconds Birmingham were ahead when Cameron Jerome shook off the attentions of Javier Mascherano to lash a swerving 30-yard effort into the top corner.
Liverpool were then awarded a penalty when Ngog got himself to the byline and looked to hurdle a Lee Carsley lunge, the Birmingham man's foot not touching the Liverpool youngster.
Carsley and Ngog exchanged views and pushes and referee Peter Walton booked both before Gerrard stepped up to drill home the penalty and snatch a point.