The Yorkshire side forged ahead through a header from in-form striker Davide Somma, who started the game after a double against Millwall at the weekend.
However, Richie Wellens pulled the Foxes level after 65 minutes and Howard kept his nerve from the spot after Neill Collins handled in the box.
The game came to life after a poor first quarter when Leeds goalkeeper Shane Higgs was forced to punch a fierce drive over the top from Dany N'Guessan after the Leicester man made room to turn and shoot from the edge of the box.
Max Gradel, making his first appearance of the season after a four-game ban, was looking lively for Leeds against his old club and his powerful right-footed drive was tipped over the top by Foxes goalkeeper Conrad Logan after half an hour.
Within a minute Gradel had laid on the opening goal when his superb first-time cross from the right was expertly glanced home by Somma.
Bradley Johnson almost doubled Leeds' advantage in the 44th minute but his angled shot after advancing into the left-hand side of the box floated just too high.
Leicester had to scramble the ball away from danger right at the start of the second half after Gradel stole into the box from the right and Higgs then spilled a low, swerving shot from Gallagher at the other end but gathered at the second attempt.
Gradel jinked his way into the box from the right side again in the 57th minute but could not apply the finish which his trickery deserved.
Leicester were not out of it though and Dutch full-back Michael Lamey's well-struck shot from 25 yards needed a flying block from Alex Bruce to prevent it testing Higgs.
The visitors levelled when some poor control from Johnson handed them possession on the edge of the box and two slick passes presented an opportunity to Wellens, who made no mistake with a low finish.
It took a stunning point-blank save from Higgs to keep Leeds on level terms five minutes later when he somehow blocked Howard's close-range effort from Gallagher's low cross from the right.
Morrison did brilliantly to head clear a Gradel cross under pressure from Somma, who then rifled over with his left foot after receiving possession from substitute Sanchez Watt.
The decisive moment came when a seemingly innocuous set-piece floated forward, bounced up and struck Leeds defender Collins on the arm, and Howard made no mistake from the spot.