N'Guessan has scored in all three of his appearances at The Valley since completing a loan switch from Millwall and further endeared himself to the home fans with the only goal 10 minutes before the break.
The hosts started brightly and might have gone in front inside the opening minute when N'Guessan's shot produced a good save from visiting goalkeeper David Grof.
Johnnie Jackson headed just wide, while Ben Hamer did well to tip over Alex Nicholls' effort at the other end, but Charlton broke the deadlock in the 35th minute as N'Guessan beat Grof to the ball to head home from Jackson's free-kick.
Walsall were almost back on terms early in the second half after Addicks goalkeeper Ben Hamer made a complete hash of Emmanuel Ledesma's delivery, only for Jon Macken to place the loose ball off target.
Bradley Wright-Phillips' 54th-minute effort lacked power and sailed harmlessly behind after Jackson's clever pass had put the Charlton top scorer through, while N'Guessan was only denied a second by Grof's smart in the 82nd minute.