Leam Richardson's men were second best for much of this encounter but showed the kind of resilience needed if the league's bottom club are to have any chance of survival.
Rovers went ahead through Arnor Sigurdsson's well-taken eighth-minute finish and it looked to be the perfect platform for a routine afternoon.
But, given the two sides have the league's worst defensive records, it was no surprise Rotherham exposed Blackburn's frailties. After a trio of superb Viktor Johansson stops, they equalised through Sean Morrison's header.
Sammie Szmodics' composed finish restored Blackburn's lead straight after the restart but Rotherham hung in and Tom Eaves' powerful header eight minutes from time gave them an improbable draw.
They are seven points from safety but it's three unbeaten for Richardson while Blackburn's wretched run continues with just one win in eight.
Rovers were ahead early after Szmodics' shot was blocked across the box and Sigurdsson controlled well before stabbing home his sixth of the campaign from 12 yards.
Johansson produced a flying save moments later to tip Harry Pickering's rasping drive over and they almost equalised in the 18th minute when a corner found Christ Tiehi but Rovers scrambled his close-range shot behind.
Rovers continued to threaten and Callum Brittain's cross found Sigurdsson but his first-time shot was blocked by Morrison, who flung himself at Semir Telalovic's shot to prevent a certain second.
Brittain was then denied by Johansson at full stretch before Szmodics sliced wide with the goal gaping.
They paid for their profligacy as Rotherham's testing corners yielded a 31st-minute equaliser when Sam Clucas found Morrison six yards out and he nodded home with ease.
Johansson was at it again in the 34th minute when he produced a stunning reaction stop to repel Szmodics' powerful low effort from the right of the area.
Rotherham's Ollie Rathbone almost grabbed a second in first-half stoppage time but curled against the crossbar and Rovers responded straight after the restart when Szmodics ran onto a James Hill pass and rounded Johansson to notch his 16th of the season.
The second half wasn't as frenetic but the Millers missed a glorious 63rd-minute opportunity to level when Sam Nombe crossed into the path of Eaves six yards out but the striker contrived to direct the ball over.
Rovers dominated proceedings without forcing Johansson into heroics like those in the first half and they were sucker-punched again with eight minutes remaining.
Sebastian Revan whipped a dangerous cross from the right onto the head of Eaves, who stooped to convert into the bottom-right corner to secure only Rotherham's third away point this season.