The Millers went to Barnet looking for the win with manager Ronnie Moore keeping the same staring eleven that had drawn at home with Cheltenham the previous Saturday.
At the start of the game the third automatic promotion place was still available, but with Bournemouth beating Burton, the Millers must now settle for a play-off place.
The Millers started brightest of the two sides, Nick Fenton won a header from a corner in the 17th minute, but Marshal could not capitalise on the chance, it being saved by Barnet keeper Jake Cole.
The 25th minute saw the Millers go close with an effort from Josh Walker, Adam Le Fondre had been brought down 25 yards from goal, and from the resulting free kick Walker struck the post.
The Millers were awarded a free kick on the right of Barnet's box in the 35th minute, Ellison's free kick caught everyone by surprise, when he stepped up and shot straight into the net to put the Millers in front.
The second half saw more of the same from the Millers, Gunning going close with a header, and Adam Le Fondre forcing a save from Cole.
The Millers rattled the woodwork for a second time in the game in the 80th minute. Ellison was put clear in the Barnet penalty area by Le Fondre, but his powerful shot hit the Post.
Paul Warne came on for the last few minutes of the game to tighten things up for the Millers, in a game in which Warrington hardly had a shot to save, and all three points going to the Millers.