Simonson began working in comics as a comic editor at Warren Publishing in 1974, and in 1980 moved to Marvel Comics editing several series including The Uncanny X-Men. In 1981 she began editing Marvel's Star Wars series and contributed to writing the stories on a few issues. Later, she became the regular writer on Marvel's series The New Mutants, X-Factor (with her husband Walt doing the pencilling), and Power Pack. In the 1990s she started working on the DC Comics series Superman: The Man of Steel, and was one of the writers involved in the storyline telling of the death of Superman.
In 1995 she wrote River of Chaos for Dark Horse comics, where she again worked with former Power Pack collaborator June Brigman.
- Star Wars (1977) 56
- Star Wars (1977) 57
- Star Wars: River of Chaos
- The Rise of a Hero