Town took full advantage of poor marking from the visitors, netting from their first two corner kicks, with Leicester's reply eight minutes from time causing a few nervous moments.
Ipswich were ahead after just two minutes when Shefki Kuqi stooped to head Jim Magilton's corner in from just six yards, standing unmarked to net his 15th goal of the season after Ian Walker had tipped over Darren Currie's shot.
Kelvin Davis made the first of what was to be several fine saves, diving to deny former Wimbledon team-mate David Connolly's 30-yarder, and moments later he made an even better save to push away Connolly's low angled drive.
Keith Gillespie fired over as Leicester continued to impress and then Davis clutched a curling Jordan Stewart free-kick just under the bar.
Against the run of play, Town went 2-0 up on 24 minutes. Ian Walker fumbled a low Tommy Miller drive behind for a corner and from Currie's delivery, the ball spun in off Mark De Vries for an own goal - the striker having been unsighted by Jason De Vos' jump in front of him.
Davis added to his fine collection of first half saves on 35 minutes with a stunning reflex block to deny Connolly once more after De Vries had nodded down a Stewart cross.
James Scowcroft, linked with a move back to Portman Road, should have punished his old team on 38 minutes but he wasted an unmarked far-post header, nodding wide from Gillespie's free-kick, before another Gillespie set-piece saw Dion Dublin's header saved by the busy Davis.
There was a blow for Ipswich in first half stoppage time when leading scorer Kuqi was stretchered off with a badly gashed left leg, and then De Vries pounced on a poor Richard Naylor back-header but Davis was out quickly to block.
De Vries shot wide in a generally quiet opening to the second half, before another ex-Ipswich player in the Leicester ranks almost gifted them a goal, Chris Makin's touch from Darren Bent's low cross just going past his own post.
Naylor glanced a header on to the roof of the net from Currie's ensuing corner, before Currie was in the right place at the other end to clear a Nikos Dabizas header off the line following a Stewart corner.
Despite a number of good chances to kill the game off, Town couldn't take them, and a nervy finale was guaranteed when Stewart curled a superb 20-yard free-kick in off the bar with eight minutes to go.
Town held on, with Bent twice guilty of wasting opportunities on the break, while Davis made another terrific save to keep out Gillespie's low drive in time added on.