Ellington, who has plundered 23 goals this season, was left on the bench after scoring just twice since February - and both of those were penalties.
Ormerod, on loan from Southampton until the end of the season, struck in either half as Wigan finished comfortable winners.
Ormerod struck first after 25 minutes when Graham Kavanagh floated over a free-kick which he headed home from six yards with the final touch coming off Leicester defender Nikos Dabizas.
Wigan created two other good chances before the break - Ormerod heading Kavanagh's corner narrowly over and then Jason Jarrett shooting wide after he stole the ball off a dithering Johannes Gudjonsson.
There was no argument about Ormerod's second just before the hour mark when he rose above Keith Gillespie at the far post to convert Kavanagh's corner with a powerful header.
Leicester then sacrificed wide man Gillespie for defender Darren Kenton which allowed Dion Dublin to join the attack.
The move allowed City to enjoy more of the game but they were never to threaten Wigan's complete dominance.
And Wigan were only denied further goals when first Kenton cleared Lee McCulloch's header off the line and then Ian Walker dived in bravely to block Jason Roberts' close-range shot.
Afterwards Jewell was full of praise for his match winner.
"Brett Ormerod has been chomping at the bit to get his chance so I was delighted to see him score twice," said the Wigan manager.
"It was a hard decision to leave Nathan Ellington out because he is our top scorer, but he has looked jaded of late and I don't think a spell on the bench will do him any harm.
"We did very well but 1-0 is always a risky scoreline so it was a relief to see the second go in."
Leicester manager Craig Levein acknowledged that his team had not performed well and warned his players they need at least one more win to keep them safe from relegation.
"They were better than us and of all the teams we've played here they have caused us the most problems," he admitted.
"We had a good penalty shout when Mark De Vries was fouled inside the box but if we had got back into the game, it would have not have been a fair reflection on the game.
"But we didn't perform and that didn't help. Even if we had they would still have been too good for us.
"We are only three points clear of the relegation zone and we should never be in this position. But we have drawn too many games and made too many mistakes.
"We've now got a big game on Tuesday night against Cardiff where a win will really take the pressure off us."