Slade, who will move into a new head of football role over the summer, saw his side fall behind to David Cotterill's low drive in the 11th minute, but Anthony Pilkington's close-range finish ensured a share of the spoils at Cardiff City Stadium.
While Slade has not always been a popular figure among the home support, there can be no denying the important work he has done to help stabilise a club so often caught up in off-the-field controversy in recent years.
He leaves a solid base for the next manager to build on, with the club's transfer embargo now lifted, and like opposite number Gary Rowett he will be left ruing a late-season stumble that ultimately ended any lingering play-off aspirations.
The Bluebirds started brightly through Craig Noone, the winger surged forward to tee up Tom Lawrence, with Adam Legzdins getting down to make the save.
Noone soon threatened again as he jinked into the box but found the Birmingham keeper level to his strike, and Cotterill showed him how it should be done moments later.
Clayton Donaldson twisted and turned on the edge of the box and when his deep cross came through to Cotterill the Wales international took a touch and despatched the ball into the bottom corner.
The lead nearly doubled seven minutes later. Matt Connolly's poor pass fell to Diego Fabbrini and the in-form Italian drove forward and unleased a curling drive which beat David Marshall but not the base of the post.
Not that Cardiff were short of chances at the other end, Legzdins had to be sharp to save at Pilkington's feet following a lovely exchange of passes with Lex Immers before a defensive howler allowed the former Norwich man to level.
Scott Malone's cross appeared to pose little danger but Jonathan Grounds found himself caught in two minds as he tried to deal with the ball facing his own goal, and Pilkington nipped in to score his ninth goal of the season from close range.
The first half rather meandered to a conclusion after an entertaining opening, but Cardiff began the second half with renewed vigour, and Legzdins was soon in action to parry a Noone strike to safety from another clever Immers pass.
The Cardiff winger was soon making another telling contribution, but this time at the other end.
Ben Turner, making his first Cardiff appearance in a year after a series of ankle problems, brought down Donaldson right on the edge of his own box and heaved a sigh of relief as he received a yellow card despite being the last man.
Cotterill took the resulting free-kick and had beaten Marshall, only for Noone to get back to cover the far post and head off the line.
The visitors had one last chance to win it late on as a defensive lapse allowed substitute James Vaughan in, but the striker was denied by the post.
CARDIFF: Marshall; Peltier, Connolly (Manga 81), Turner, Malone; Noone, O’Keefe, Whittingham, Lawrence (Harris 73); Pilkington, Immers (Zohore 66). Subs: Moore, John, , Ameobi, Saadi
BIRMINGHAM: Legzdins; Spector, Morrison, Robinson, Grounds; Adams (Gleeson 71), Kieftenbeld, Davis (Solomon-Otabor 79); Cotterill, Fabbrini (Vaughan 85), Donaldson. Subs: Trueman, Caddis, Shotton, Brock-Madsen