Rotherham United led thanks to a stunning free kick from youngster Stephen Brogan but McGleish grabbed his 16th of the season in bizarre fashion.
It came in the 56th minute when he curled in a high cross to the far post, only for the ball to drop in over the despairing Millers' keeper Andy Warrington..
It stunned Millmoor's biggest crowd of the season, but Paul Lambert's Wycombe richly deserved their point.
Rotherham could have been in front after two minutes when leading scorer Derek Holmes saw his header held by keeper Frank Fielding.
Pablo Mills went close with a dipping shot and was a fraction off target with an audacious long range effort.
The home side took the lead with a tremendous opener after 14 minutes, with Brogan catching the Chairboys unaware with a fabulous free-kick.
Wycombe responded well after the set back. A blistering shot from McGleish was beaten away by Andy Warrington, and John Sutton shot over from close range.
However the Yorkshire side twice came close to a second. A through ball from Mills opened up the Chairboys but Chris
O'Grady's angled shot was saved, and seconds before the break Holmes' header thudded against the bar.
Wanderers stared brightly after the break and were rewarded on 56th minutes thanks to McGleish's curling cross bringing them level.
The setback rocked Rotherham and Wycombe boss Lambert brought on Leon Knight as an extra striker as the visitors hunted for a late winner.
However the home side could have been in back front two minutes later when Holmes' goalbound header was superby saved by Fielding.
Another Stephen Brogan free kick triggered a double save from Fielding, and the tricky RyanTaylor saw an audacious chip fly just over.
A draw was a fair result, but Lambert's side will travel back to Buckinghamshire much the happier side, especially after their impressive fightback on the boggey pitch.