The striker, an £8million signing last summer, headed home his 28th goal of the campaign at St Andrew's to ensure Blackburn - all but mathematically safe going into the final day - finished the Championship season four points and five places above the drop zone.
And with the Lancashire outfit only managing 55 goals in total, Rhodes' exploits have proved pivotal to their bid to avoid back-to-back relegations - a fate which Wolves have failed to avoid.
The draw ends a season to forget for Blackburn, who have gone through an astonishing six managers since the opening day.
On-loan West Ham midfielder Ravel Morrison's neat skill and finish had put Birmingham into the lead just before at half-time, with Rovers momentarily out of the bottom three merely due to their beneficial goal difference.
The Blues, who have endured a difficult year themselves, ended the season just about in the top half with a mid-table 12th-placed finish and a final record of results which says very much about where they currently stand - 15 wins, 16 draws, 15 defeats.
Nikola Zigic found himself in a good position for Birmingham midway through the first half but could only hit the side-netting.
Caddis' terrible back pass then put Butland in all sorts of trouble with Rhodes closing in but the England goalkeeper, making his final Blues appearance before his departure for Stoke, cleared the danger.
Sandomierski got down well to his right to tip Nathan Redmond's low shot around a post as the home side continued to look more likely to break the deadlock, Chris Burke firing narrowly wide.
And Birmingham finally got the goal they deserved just before half-time as Morrison showed neat skill before converting into the bottom corner from just inside the penalty area.
As in the first half, there was very little to get excited about at the start of the second period.
But all that changed, especially for the travelling contingent, in the 66th minute.
Morten Gamst Pedersen's long throw was flicked on by Grant Hanley and Butland did well to save from David Jones but Rhodes was on hand to head home the rebound.
Birmingham, below par after the break, huffed and puffed as they looked to retake the lead but were let down by poor decision-making and a lack of quality in the final third, with manager Lee Clark an animated subject on the sidelines.
And as the game petered out, it was difficult to see anything other than a third successive 1-1 draw between the two sides.