Jan Bednarek and Che Adams scored first-half goals for the home team either side of a Jonny Evans strike for the visitors to lead 2-1 at halftime.
A medical emergency in the crowd during the break forced a delay to the second period but once the action got back under way, it was the visitors who were much the brighter as Maddison soon equalised.
The draw moves Leicester up to 19 points, while Southampton are on 15 points.
“We took too long to get going in the game,” Leicester manager Brendan Rodgers told BBC Match of the Day. “We lacked concentration, we made a change at halftime and changed the attitude and mentality of the team.
“Second half was a different game for us and at the end we had the clear chances to win.
“We have an incredible resilience when we fall behind — we found a way to come back. The mentality and attitude was totally different in the second half.”
The home side were in front inside three minutes when Leicester goalkeeper Kasper Schmeichel saved brilliantly from Mohamed Salisu’s shot but Bednarek reacted quickest to turn the ball home.
It was the third time in four games that they had taken the lead inside five minutes.
Leicester, who have not kept a clean sheet in the Premier League since a 1-0 win over Wolverhampton Wanderers on the opening day of the campaign, equalised midway through the first half.
Home goalkeeper Alex McCarthy could only parry Wilfred Ndidi’s shot into the path of Evans, who had a simple finish.
Leicester-born Adams, a boyhood fan of the Foxes, headed the home side back in front when he connected with Nathan Redmond’s deflected cross to give them a 2-1 halftime lead.
After the 33-minute interval, the visitors got back on level terms early in the second period when Maddison twisted and turned in the box and drilled the ball low past McCarthy at his near post.
Leicester forward Jamie Vardy had an excellent chance to grab the winner when he was one-on-one with McCarthy, but produced an uncharacteristically wild finish over the bar.