The champagne looked destined to remain on ice until the striker rose majestically above the United rearguard to power home a header from a Max Gradel corner. The result means Leicester will go up at the first attempt if MK Dons fail to beat Bristol Rovers.
City were the better side and had Leeds under the cosh from the start with a Lloyd Dyer effort deflecting to safety off Sam Sodje and goalkeeper Casper Ankergren diving at full-stretch to keep out Gradel's 20-yard drive.
Ankergren then beat away an Andy King header before Leeds almost silenced the home crowd with a bizarre goal, but Gradel came to Leicester's rescue when he cleared off the line after David Stockdale had punched a Robert Snodgrass corner against the underside of the bar.
After the break Stockdale had to make a double save to keep out Richard Naylor's close-range header before the busy Ankergren produced good stops to keep out Andy King and Matt Fryatt.
Ten minutes from the end Andy Robinson evaded Jack Hobbs to fire in a 20-yard shot which Stockdale was forced to tip over. And the game appeared to be heading for a stalemate until Howard intervened with his 13th strike of the season.