The defender converted Aaron Cresswell's corner in the fifth minute for the only goal of a game that showed why both teams have struggled for consistency this season.
Ipswich were happy to sit on their lead and invite pressure, while Charlton found it difficult to pass to each other and - bar a Rhoys Wiggins shot that was palmed on to the post by Dean Gerken - could not create anything meaningful and remain with just seven goals at home all season.
Ipswich started at an electric pace and could have had four in as many minutes before Smith put them in front against a sleepy Charlton.
David McGoldrick was put clean through by Paul Anderson only for Wiggins' last-ditch tackle to prevent Town's top scorer and concede a goal kick.
From the resulting corner, Ben Alnwick, starting in place of the injured Ben Hamer, brilliantly saved Smith's header.
If that was good though, then his double save from the next corner was extraordinary as he flung himself across goal to stop Darryl Murphy's header and then got up quickly to block Christophe Berra's fierce follow-up shot.
Eventually though he was beaten as Charlton again failed to deal with a corner as Smith headed into the ground and beyond Alnwick from Cresswell's delivery.
The first five minutes promised a goal glut but the rest of the game failed to live up to the early hype.
Charlton did finally wake up and Dale Stephens headed just wide.
Simon Church was denied at the back post by Cole Skuse and Wiggins' cross shot almost produced an equaliser only for him to see Gerken pushed it on to the post.
The Addicks, despite struggling to keep hold of the ball, continued to have the better chances at the start of the second half as captain Johnnie Jackson wriggled free in the box only to shoot tamely at Gerken.
Ipswich seemed content to soak up the pressure and hit the home side on the break, Paul Anderson side-footing into Alnwick's gloves at the other end.
Charlton pushed for an equaliser but were found wanting when they entered the final third, Cameron Stewart's low shot from distance, easily held by Gerken, was the best they could muster.
Danny Green, Joe Pigott and Marvin Sordell were all introduced in the hope of finding a breakthrough by Ipswich stood firm as Charlton wasted countless good positions with poor passes and poor decisions.
Tempers boiled over in injury time as the Addicks wasted another free kick and Michael Morrison and Frank Nouble were booked for their parts in an ugly flare-up.