Chasing a seventh successive home league victory, Leeds were unchanged, although Matthew Kilgallon had a place on the bench after injury.
Norwich, who had gone four away league games without a win, had left-back Adam Drury returning after suspension and striker Robert Earnshaw had to be content with substitute duty.
Norwich almost conceded a 17th minute own goal when Gary Kelly's cross cannoned off Carl Robinson leaving keeper Robert Green to make a diving save.
But Leeds opened the scoring three minutes later. Robbie Blake found Lewis to the left of goal, the American fluffed his shot but the ball bobbled to Rob Hulse who prodded home his 12th goal of the season from six yards.
Hulse would have scored again five minutes before half-time had it not been for an excellent save by Green who clawed away the striker's header from Lewis' free-kick.
Leeds dominated the first half, with Hulse powerful in attack, Liam Miller energetic in midfield and Kelly repeatedly darting forward to send in crosses.
Kelly also found time to shackle his former Leeds team-mate Darren Huckerby.
Neil Sullivan waited until the 54th minute to make his first save by keeping out Gary Doherty's flicked shot from 15 yards.
Leeds paid for stepping off the gas when the Canaries equalised on 57 minutes. Simon Charlton's long ball forward found Andy Hughes in acres of space on the right and he raced into the box to shoot powerfully under Sullivan's body.
Then, after Paul McVeigh had wasted a clear chance, the former Tottenham academy player latched on to Huckerby's low cross and found the bottom left corner of the net to stun the Leeds fans.
But Lewis curled in a superb 20-yard free-kick in the 90th minute to rescue a point.
Sean Gregan's booking for a foul on Leon McKenzie was his 10th of the season and the defender faces a two-match ban starting in a fortnight.