Ipswich had looked to be heading for a deserved win when Jason Scotland netted in the 58th minute.
But Simpson, making his first appearance since January, nodded in a delightful header five minutes from the end to extent Hull's unbeaten run in the league to eight matches.
Ipswich were forced into a change as on-loan Jimmy Bullard was ruled out due to the terms of his deal from his parent club.
Andy Drury came in for Ipswich, while Hull boss Nigel Pearson kept faith with the team that edged past Preston last week.
The hosts created the first chance when Connor Wickham, fresh from his treble at Doncaster, held the ball up to lay off for Lee Martin.
Martin latched on to the pass but his drive from long distance flew over Brad Guzan's crossbar.
The teenager was the catalyst behind every Ipswich attack and the winger skipped past Liam Rosenior to force a corner for his side.
Hull weathered the early storm but the pace with which Wickham ghosted past the Hull right-back was an indication of the problems the away side would face.
They hit back when Cameron Stewart forced a save from Marton Fulop in their first foray into Ipswich territory.
Tijani Belaid nearly pinched the lead for Hull with an audacious free-kick from 40 yards that grazed the top of the goal.
Ipswich always looked threatening and a fierce hit from Grant Leadbitter brought a decent save from Guzan.
Wickham went closer to putting his side in front until Andy Dawson made use of all his experience to put in a superb goal-saving challenge.
That helped Hull through to half-time unscathed and Pearson's men were able to regroup for the second period.
They stifled the threat of Wickham's pace but the 17-year-old still carried enough menace to lay on a goal for his team in the 58th minute.
His pass found Scotland on the edge of the box and the big striker was given enough room to get his shot away.
The strike looked a tame one but it was firm enough to creep past Guzan as Scotland celebrated his ninth goal of the season.
Aaron Mclean offered his first significant contribution of the afternoon to warm Fulop's hands but Hull were in dire need of impact as they began the search for a leveller.
And it was City's forgotten man, Simpson, who snatched a point for Pearson's men.
The summer signing from Arsenal came on for Belaid and needed seven minutes to make his mark on the clash.
Latching on to a Corry Evans cross from the left, Simpson connected from 12 yards to direct a header past Fulop and grab his team a draw.