On a nervous afternoon in the North-East, the home side 2-1 triumphed and that coupled with Ipswich's 1-1 draw at Leeds sent Weraside into ecstasy.
It didn't look like it was going to script however, when Leicester claimed a fourth minute lead through Alan Maybury.
He caught the home side cold when he latched on to City skipper Danny Tiatto's pass from midfield to outmuscle Sunderland right-back Stephen Wright, before surging into the box to curl a right-foot shot beyond 18-year-old debutant goalkeeper Ben Alnwick.
Leicester had come out of the blocks far brighter, yet Marcus Stewart had already spurned a chance to put the home side in front when he volleyed wide.
The end to end opening continued with David Connolly forcing Alnwick into a sharp save in the tenth minute and then the keeper had to block brilliantly again two minutes later when Mark De Vries poked towards goal following a corner and the keeper kept it out with his foot.
Sunderland were rocking, but found their feet and Liam Lawrence saw City keeper Ian Walker deny him at the near post from a firm right-foot shot on the quarter hour, before Julio Arca set up Andy Welsh but again his effort was blocked out for a corner.
The Black Cats got the leveller they deserved in the 23 min with a lightening break that saw Chris Brown feed striker partner Marcus Stewart and Sunderland's leading scorer made no mistake with a emphatic left foot finish for his 17th of the season.
Despite getting back on level terms the Black Cats defence was still shaky and sub Stefan Moore left his marker for dead with a flick on the turn before passing to Stephen Hughes in the box, but Wright got back with an heroic block.
Sunderland lived on their nerves to keep their scores level at the break and the game that had little anger in it threatened to boil over when Dion Dublin chopped down Chris Brown close to the halfway line.
Brown reacted angrily and jumped up to remonstrate and the two players' heads clashed. Manager Mick McCarthy came on to the pitch to control his angry striker and both Dublin and Brown received yellow cards.
That came on 55 minutes but it was all forgotten four minutes later when Steve Caldwell headed the goal that send Sunderland back into the big time. He got up highest in the Leicester penalty area to power home a header from Lawrence's left-wing corner to spark the party.
Foxes boss Craig Levein sent Dublin up front in a bid to get back into the game, yet it was little forward Connolly who had the visitors' next best chance when he drilled a fierce shot from 25 yards that Alnwick spilled before skipper Gary Breen picked up the pieces to clear.
With news reaching the home crowd that Ipswich were only drawing at Leeds the celebrations were well underway.
Sub Stephen Elliott went close to extending Sunderland's lead but there were to be no more goals and only an anxious two further minutes for Ipswich's result to be confirmed before Sunderland's players and management took to the field for a joyful lap for honour.
This was a sweet moment for McCarthy, who finally buried the bitter memory of losing the first 11 games in charge of Sunderland and he can now start planning for the top-flight.
However, he will surely hope his club's season can be capped by clinching the title, which could happen if Sunderland win at West Ham on Friday.