The Millers dominated the clash of the promotion challengers in the early stages and stunned the visitors with a goal after 10 minutes.
Ben Pringle's corner was headed clear by Orient, but only as far as Mark Bradley. He gave the ball to Pringle again and from his cross Wes Thomas turned a header into the net.
But the O's gradually fought their way back, inspired by Dean Cox. His shot after 16 minutes was only parried by Adam Collin and two follow up shots were blocked in a hectic goalmouth scramble.
But Rotherham continued to press forward. Pringle curled a free-kick just wide and Revell brought a full stretch save out of Ben Alnwick before Cox threatened at the other end, firing a shot just wide.
Alnwick saved the visitors again after 60 minutes when substitute Tom Hitchcock broke clear as the keeper stuck out a foot to turn his shot for a corner.
But Orient's pressure finally paid off after 76 minutes. Chris Dagnall's cross from the left cleared the entire Rotherham defence and picked out Moses Odubajo completely unmarked on the far side and he drilled a shot past Collin.
But with time running out Revell netted for the third time in a week, firing home from 20 yards with an expertly taken goal when everyone else had settled for a draw.
Source PA