McCulloch's clinically-taken goal had given Wigan the perfect early tonic and Ellington then made sure they got back to winning ways.
The visitors badly needed a morale-boosting victory having previously suffered three consecutive defeats which pushed them outside the automatic promotion places after the last round of matches.
But Ipswich and Sunderland, above Wigan at the start of play, both lost to make the Latics' victory all the more sweeter as they moved back to second in the Coca-Cola Championship table.
Neil Warnock's side had been beaten only once in 17 league matches prior to this game but they were unable to avenge the 4-0 drubbing they suffered at the JJB Stadium in September.
Wigan started brightly and they took the lead after just seven minutes.
Jimmy Bullard's outswinging corner found McCulloch and his first-time volley flew past Blades goalkeeper Ian Bennett.
The home side were stung into action by that setback and attempted to hit back immediately with Nicky Eaden clearing Andy Liddell's dangerous free-kick and then Alan Quinn sending a 20-yard shot over the Wigan crossbar.
But it was the visitors who went agonisingly close to doubling their advantage after a quarter of an hour when Leighton Baines rattled the woodwork with a fine left-foot shot from 20 yards.
As Wigan continued to push, Bennett saved well from Ellington after 18 minutes and then denied McCulloch just moments later.
The home side were struggling to carve out clear-cut chances and when Chris Morgan did get sight of goal midway through the first half his fiercely-struck shot was blocked by Ian Breckin.
Danny Cadamarteri was on target with a 20-yard effort 10 minutes before the interval but Wigan goalkeeper John Filan parried it before Liddell sent his shot sailing over the crossbar.
Wigan were forced into a change just before the break when Michael Flynn replaced the injured Bullard.
Wigan started the second half as strongly as they had the first and the home side were indebted to Bennett as he blocked a close-range shot from Roberts just four minutes after the resumption.
Sheffield United continued to be thwarted in their efforts to get back on terms and Phil Jagielka crashed another long-range shot wide on the hour.
But it was the visitors who continued to enjoy the better of the exchanges with Ellington sending a header just over from a Roberts corner three minutes later and the same player put the game beyond the home side's reach after 72 minutes.
Flynn's corner found Ellington who made no mistake with a close-range header to double Wigan's advantage.