The actress, who voiced Bart Simpson's teacher Mrs. Krabappel on the hit show, had been battling poor health for many months, but producers were hoping Wallace would be back and writers were working on a major storyline for her character.
Cartwright, who voices Bart on the cartoon series, has remembered her late co-star "a ray of light".
The actress tells The Hollywood Reporter, "She’s in 178 episodes - a lot more than people might think. That’s more episodes than most standard shows. Marcia was always a very big part of the group. Always a treat. The room was always a little bit better with her in it.
"She had recorded some upcoming episodes, I don't know how they will use it. I don’t know what they’re going to do with the character. I’m curious to see what they do."