He had been without a goal since December 12 when he scored in a 4-2 win at Bradford City but he has finally ended his goal drought.
"I was beginning to think the next one would never come," said Ellison. "I'd got nine when I scored at Bradford and never thought I would be kept waiting so long to get into double figures."
His return to the goal trail in the 35th minute provided three precious points which kept Rotherham out in front of the eight clubs chasing the four places.
Rotherham manager Ronnie Moore said: "It was a big win and we know that one more win guarantees us, or even two more points, regardless of what anyone else does.
"He deserved it but it wasn't easy. Barnet are fighting for their lives and you could see that at the end when they threw everybody forward."
Josh Walker had already hit the post with a superb free-kick before Ellison's winner.
That also was from a free-kick but was an in-swinger from out on the right and no-one could get a head to the ball as it carried on into the far corner of the net.
Ellison should have had another one late on with only the goalkeeper to beat but his effort hit the post.
Barnet couldn't find a way through to Andy Warrington chiefly due to some sterling work from central defenders Ian Sharps and Nick Fenton.
Barnet: Cole; Devera (O'Neill 86), Breen, Gillet, Lockwood; Adomah, Hyde, Hughes (Upson 56), Jarrett (Leach 69); Furlong, O'Flynn. Unused Substitutes: James, Livermore, Deverdics, Carpenter.
Rotherham United: Warrington; Lynch, Sharps, Fenton, Gunning; Law, Mills, Walker (Bell-Baggie 44, Cummins 73), Ellison; Marshall (Warne 90), Le Fondre. Unused Substitutes: Green, Haggarty, McAllister, Annerson.
Referee: S Rushton (Staffs).
Man of the match: N Fenton.
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