Leicester's five-match winning sequence in the Championship was brought to a halt with the draw.
The Foxes, who have now moved to the top of the table on goal difference, were aiming to record a sixth successive league win for the first time since a club-record equalling seven in 1993.
And the visitors' first-half display certainly deserved just that but they found England prodigy Jack Butland in superb form while Martyn Waghorn also blazed over a golden opportunity from close range, much to the dismay of 4,000 travelling supporters.
Birmingham, second best, duly capitalised against the run of the play in first-half injury time as Lovenkrands converted a great cross from Marlon King for his third goal of the season.
Lowly Blues subsequently found a new-found confidence amid a quieter second half, but Leicester - who looked set to draw a blank for the first time this season - drew level in the 86th minute when Marshall's 30-yard effort crossed the line off the inside of a post.
To make matters worse for Birmingham, Jonathan Spector was given his marching orders in injury time.
Ravel Morrison, whose attitude had again been brought into question since his season-long loan arrival from West Ham, was handed his first Birmingham start since August amid four changes and duly impressed, the Foxes also included three new faces from last time out before the international break.
Birmingham boss Lee Clark spoke pre-match about the need for his side to start positively but he would have been furious at the way in which they gave possession away straight from kick-off, conceding a free-kick on the edge of their area which was comfortably saved by Butland.
Blues, having got a better foothold on proceedings, saw on-loan full-back James Hurst escape punishment following a challenge on Lloyd Dyer in the penalty area before Waghorn forced a solid save from Butland.
Dyer did find the net only to be flagged offside as the Foxes posed a more dangerous threat in the final third, Butland producing a routine stop to deny Anthony Knockaert from distance before Andy King lashed narrowly wide.
Leicester's best opening of the first half arrived in the 33rd minute yet Waghorn somehow fired over Andy King's cross from six yards.
Birmingham were providing very little threat in attack, with Kasper Schmeichel finally forced into action to save from Nathan Redmond in the 38th minute.
Butland then twice kept out talented Frenchman Knockaert, the second a superb stop just before half-time.
But there was still time for the home side to take the lead. Marlon King latched on to Hurst's pass and fired a great cross into the area which was expertly converted by Lovenkrands.
Schmeichel denied King when clean through early in the second half before Redmond blazed a free-kick off target for Blues.
Butland continued his heroics with another super stop to keep out Waghorn, but chances were coming at a premium compared to the opening 45 minutes.
Substitute Wade Elliott tested Schmeichel as the game entered the closing stages before Marshall drew Leicester level out of nowhere, his shot from distance going in off the inside of a post.
Spector then saw red for what appeared to be a second yellow card offence, and there was still time for Butland to produce another great stop to keep out Marshall's goalbound free-kick.