Warnock came to the club on a 16-game mission to wipe out a two-point gap to safety and get the Millers' ahead above water.
Three games into his reign and things got even worse as they slipped to six points behind MK Dons and having not scored a goal under him yet, the Millers' prospects looked even bleaker.
Then as February game to a close the tide turned massively as Warnock worked his magic and the Millers embarked on a staggering, coupon-busting run of form that ultimately led them to safety with three games to spare.
Here we chart how their survival mission played out.
February 23
Rotherham followed up a defeat at Burnley with a limp showing against an average Reading side, going down to Hal Robson-Kanu's second-half goal and with no offer of a response things looked terminal for them.
However, in a potentially crucial twist, for large parts of the game they were heading eight points adrift as MK Dons were beating 10-man Huddersfield. But the Terriers scored a last-gasp leveller to bring the deficit back to six and the momentum changed.
20. Bristol City 34 pts
21. MK Dons 32 pts
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22. Rotherham 26 pts
February 28
Starting the day six points behind MK Dons, in a game that Rotherham simply had to win, they delivered the goods as Matt Derbyshire and Danny Ward strikes either side of an outrageous equalising penalty for Brentford gave them a valuable three points.
You could be forgiven for thinking it was April rather than February when news of MK Dons' late loss to Blackburn came through as it was greeted with a huge cheer from the Millers support, who knew just how vital that might be. At half-time they were seven points from safety, but by the time the clock turned 5pm that had been cut to three.
20. Fulham 36 pts
21. MK Dons 32 pts
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22. Rotherham 29 pts
March 5
In the first of their coupon-busting wins, the Millers enjoyed more success at Hillsborough and gave Warnock a winning visit to one of his favourite hunting grounds, thanks to Matt Derbyshire's first-half goal.
Although a great win, the Millers will have felt disappointed as MK Dons also won, seeing off QPR, to ensure the gap stayed at three points.
20. Bristol City 37 pts
21. MK Dons 35 pts
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22. Rotherham 32 pts
March 8
Middlesbrough were the latest promotion chasers to come unstuck as Lee Frecklington's 88th-minute goal earned a 1-0 win for Rotherham, giving them a third straight second-tier victory for the first time since 2003.
MK Dons registered a point in a dour 0-0 clash at Charlton to keep out of the relegation zone, but the gap was down to one.
20. Bristol City 37 pts
21. MK Dons 36 pts
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22. Rotherham 35 pts
March 12
It looked for all the world like the unbeaten run would come to an end against Derby as Rotherham found themselves 3-0 down with 10 minutes to go. Cue one of the greatest comeback's in the club's history as Danny Ward and Leon Best's brace earned the unlikeliest of points.
Millers fans would have hoped might have been enough for them to get out of the dropzone, but MK Dons were also busting coupons with a draw at Hull.
20. Fulham 38 pts
21. MK Dons 37 pts
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22. Rotherham 36 pts
March 19
There was no sign of the amazing run ending as a gruelling run of fixtures ended for Rotherham with another brilliant result. Leon Best's only goal of the game won the three points at play-off chasing Ipswich.
And that was enough to finally get them out of the bottom three as results went in their favour for a change, with MK Dons losing to Brighton and Fulham going down to Bristol City.
20. Rotherham 39 pts
21. Fulham 38 pts
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22. MK Dons 37 pts
April 2
Even a two-week international break did not stop Rotherham's momentum as they made it five wins from six in a dramatic encounter with Leeds which ruined Steve Evans' return to New York. Greg Halford's 89th-minute penalty settled it after both men had a man sent off.
With Fulham and MK Dons facing off, the Millers knew they would be out of the bottom three whatever happened against Leeds, but with Fulham winning their lead over MK extended to five.
20. Rotherham 42 pts
21. Fulham 41 pts
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22. MK Dons 35 pts
April 5
Rotherham again highlighted their fighting spirit as they earned a draw in testing circumstances at Bristol City. They made light of a hostile environment by taking an early lead through Matt Derbyshire, though succumbed to a second-half equaliser - only the second time they surrendered a lead under Warnock - when Peter Odemwingie slammed home.
Fulham picked up a fine win at Preston to haul themselves further away from danger while MK Dons continued to falter as they lost at home to Wolves.
20. Bristol City 44 pts
21. Rotherham 43 pts
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22. MK Dons 37 pts
April 9
This had long been designated as the key fixture which Rotherham dare not lose and they put on a fine show, wiping the floor with their nearest rival and landing a effectively fatal blow. It started superbly after just 54 seconds with Matt Derbyshire's opener and went on to get even better as further goals from Leon Best, Kirk Broadfoot and Richie Smallwood made it an afternoon to remember.
With Bristol City and Fulham also winning, it was a nightmare afternoon for the Dons who slipped to a damaging nine points from safety, making it a staggering 15-point swing in six weeks.
20. Nottingham Forest 46 pts
21. Rotherham 46 pts
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22. MK Dons 37 pts
April 16
Rotherham posted their longest unbeaten run in the second tier since 1982 after a stalemate with Nottingham Forest at New York. Millers defender Richard Wood missed a number of chances to register another three points, but it was still nine unbeaten for Warnock's men and six without defeat at home.
MK Dons finally stopped the rot, thanks mainly to Alex Revell's unlikely penalty save in a 1-1 draw at Preston, but it was wins they needed and they remained nine points adrift.
20. Fulham 47 pts
21. Rotherham 47 pts
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22. MK Dons 38 pts
April 19
This was the first time Rotherham could have got the job done, but their failure to beat Huddersfield in a 1-1 draw meant that it would go to their next game. Greg Halford's early goal was cancelled out by Nahki Wells and neither side could find a winner, meaning the Millers' unbeaten run extended into double figures.
An unlikely point for MK Dons at Sheffield Wednesday meant that they prolonged their hopes of the impossible and denied the Millers safety in front of their own fans.
20. Rotherham 48 pts
21. Bristol City 48 pts
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22. MK Dons 39 pts
April 23
Rotherham finally got the job done as they equalled an 11-game second-tier unbeaten run set by the 1965-66 team in a 0-0 draw at Wolves. It was not a classic and their miraculous achievement perhaps deserved a better ending, but no one will care. Warnock the Messiah!
The Millers' survival was ensured as the MK Dons slipped to a 4-1 defeat to Brentford in front of their own fans, meaning they are heading back to League One just one year after winning promotion.
19. Rotherham 49 pts
20. Bristol City 49 pts
21. Fulham 48 pts
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22. MK Dons 39 pts
