Tonge, who spent a large chunk of his career under former Sheffield United boss Neil Warnock, fired home a swerving 25-yard shot in the 76th minute to cancel out Jay Bothroyd's first-half header and deny Wednesday a first win in eight league matches.
But despite rescuing a point with a much-improved second-half display, Leeds are sure to find themselves in serious trouble from the game's authorities after the mindless antics of one fan in particular, who celebrated Tonge's fine equaliser by running on to the pitch and hitting Wednesday stopper Chris Kirkland in the face with two hands.
Riot police had earlier filtered out to try and diffuse ugly scenes in the away end prior to Tonge's strike, with bottles thrown between baying sets of home and away supporters.
Leeds boss Warnock, returning to his home city for the first time since former club Crystal Palace triumphed over the Owls at Hillsborough in an FA Cup tie in 2010, will have been grateful for Tonge's rescue act after his side stretched their unbeaten run to five matches despite being outplayed for long periods.
Wednesday have now failed to win any of their last eight league games, collecting only two points in the process and the pressure is mounting on manager Dave Jones.
Irish midfielder Paul Corry made his league debut for the Owls and defender Daniel Jones returned to the starting line-up, while Leeds were unchanged from the side that beat Barnsley last time out.
Wednesday made the more promising start. Chris O'Grady headed straight at Paddy Kenny in the sixth minute and the former Sheffield United goalkeeper let Bothroyd's fierce 20-yard drive slip through his hands and on to the crossbar soon after, with the ball bouncing down a yard from his goalline.
Wednesday skipper Anthony Gardner then spurned a gilt-edged chance when he headed Bothroyd's free-kick over the crossbar with only Kenny to beat as Leeds rode the early storm.
Leeds responded with a fine free-kick from another former Sheffield United player, Michael Tonge, whose curling effort from 25 yards following Gardner's foul on El-Hadji Diouf had Owls keeper Chris Kirkland scrambling to palm clear at full stretch.
Leeds were given a real let-off in the 23rd minute by referee Eddie Ilderton, who somehow failed to see Leeds forward Luciano Becchio handle the ball when diving in his own penalty area to head clear Bothroyd's 23rd-minute corner.
But Wednesday, belying their lowly status, secured the lead they deserved two minutes before the break.
Long-throw specialist Michail Antonio launched a missile into the Leeds box from the left and Bothroyd rose highest to head home unopposed, low into Kenny's right-hand corner.
Leeds midfielder Rodolph Austin, who arrived back in Leeds this morning following international duty with Jamaica, made way for David Norris at half-time.
Leeds were more purposeful after the restart and went close to an equaliser through another free-kick from Tongue after Gardner had been booked for his high tackle on Diouf.
But although the visitors spent longer periods in Wednesday's half, they failed to create any clear-cut chances and had it not been for Leeds skipper Lee Peltier's excellent block, Bothroyd's shot from Antonio's cutback would have found its target.
Peltier was replaced by forward Luke Varney, who spent three spells on loan at Hillsborough, in the 66th minute, but it was the home side who threatened again when Antonio's shot following a defensive mix-up was deflected for a corner.
The atmosphere turned ugly at the Leeds end with 20 minutes to go, with extra police required to quell an angry exchange between both sets of fans intent on throwing bottles.
Tonge's brilliant equaliser in the 76th minute following Aidy White's lay-off then prompted some Leeds fans to pour through fencing, with one supporter run round in front of Kirkland's goal before pole-axing the Wednesday keeper by pushing both hands into his face.
Kirkland required treatment before the game could resume and although Owls substitute Danny Mayor went close with a shot blocked by Jason Pearce in the closing stages, the home side had to settle for a point.