The Foxes were good value for their win as they out played and outfought Millwall to end Kenny Jackett's side's three-match winning streak.
Hitman Howard's 22nd minute strike from the edge of the box left David Forde standing as it nestled in the bottom corner.
A second before, the home side had strong appeals for a penalty waived away as full-back Joe Mattock appeared to bundle over Marc Laird following Tony Warner's fumble from James Henry's fizzing shot.
A desperate last-ditch tackle by Richard Duffy stopped Howard handing the visitors the lead with just three minutes on the clock after Tom Cleverley's low cross.
Having fired his side in front, Howard was lucky to stay on the pitch after referee Anthony Taylor only showed a yellow card for a blatant elbow on Tony Craig ten minutes before the break.
The home side started the second half with the upper hand, having thrown on Ashley Grimes into a four-four-two formation. A brilliant cross from the right by Henry almost found Grimes at the front post, but Warner fumbled behind for a corner.
Lions keeper Forde kept his side in the game with a fine point-blank save to deny Cleverley who found space in the box on 66 minutes.
Grimes had a great chance to pull the Lions level when he forced a fine save from Warner having got in behind the Foxes defence after a mix-up.
Matt Fryatt then raced immediately up the other end to rattle Forde's far post with a sidefoot effort with the game still delicately in the balance.
But the Foxes held on for a fine win and prevented the Lions becoming the only side to do the double over the Walkers Stadium outfit this season.