The Foxes made it 21 league games unbeaten as they moved onto 89 points - two more than Cardiff won the division with last season - and will be up if QPR lose at Bournemouth and Derby fail to beat Middlesbrough on Saturday.
Knockaert's free-kick settled the game after Riyad Mahrez's third goal since joining from Le Havre in January was cancelled out by Michail Antonio's solo effort in the first half.
Foxes boss Nigel Pearson made five changes to the side that earned a 2-2 draw at Wigan on Tuesday, with Jeff Schlupp, Danny Drinkwater, Matty James, and Mahrez coming in.
Wednesday manager Stuart Gray, whose side were thrashed 4-1 at home against Watford on Saturday, replaced Jeremy Helan and Benik Afobe with Antonio and Caolan Lavery.
Leicester made the brighter start and should have been ahead after just five minutes when David Nugent's endeavour down the left channel allowed him to play in Knockaert, who blazed wide from 12 yards out.
The Foxes were in front five minutes later though, with Jeff Schlupp, Knockaert and Chris Wood linking up impressively for the latter to play in Mahrez.
The winger still had plenty to do, but cut inside his marker and curled a low left-foot shot into the far corner.
Wednesday steadily began to play their way back into the match, and the lively Antonio saw a fierce 25-yard effort kept out by Kasper Schmeichel on 24 minutes.
At the other end Knockaert bent a 20-yard shot over the bar, and just past the half-hour Wood played in Nugent, whose low effort was inches wide of the far post.
The Owls levelled eight minutes before half-time, and deservedly it was Antonio with the goal.
The former Reading winger cut in from the left flank and fired a 20-foot effort into the bottom corner, although Denmark international Schmeichel should have done better having got a hand to it.
Knockaert put Leicester ahead again just after the hour mark - the Frenchman bending in a tremendous free-kick from 20 yards after Kieran Lee clumsily brought down Mahrez on the edge of the box.
Ritchie De Laet played in Nugent five minutes later, but the ex-Portsmouth man scuffed his shot wide attempting to double the hosts' advantage.
Wednesday pressed for an equaliser and Chris Maguire volleyed a Joe Mattock corner wide from 20 yards 18 minutes from time.
However, the visitors were unable to create a clear sight of goal until stoppage time - when Lee and Liam Palmer saw their efforts blocked during a scramble in the box - as Leicester's march towards the top flight neared its conclusion.