Simonson has won numerous awards for his work and has influenced artists such as Arthur Adams and Todd McFarlane.

[3][4] Having already developed an interest in Norse mythology prior to discovering Stan Lee and Jack Kirby's take on the hammer-wielding deity,[5] it became Simonson's favorite title, one that he read for four years.

[3][4] From this he realized that drawing comics was more fun, and more feasible as a career than working outdoors in hot weather as a geologist or paleontologist, despite harboring a love for the latter that continued the rest of his life.

[4] In 1967, while in college, Simonson began writing his own epic story starring Lee and Kirby's version of the character, featuring Surtur and the Odinsword.

After meeting with Goodwin, Simonson went to DC's coffee room, where he saw Howard Chaykin, Michael Kaluta, Berni Wrightson and Alan Weiss sitting together.

[3] At one point Simonson lived in the same Queens apartment building as artists Allen Milgrom, Howard Chaykin and Bernie Wrightson.

'"[8] Simonson's first professional published comic book work was illustrating writer Len Wein's story "Cyrano's Army", which appeared in DC's Weird War Tales #10,[3][9] which was cover-dated January 1973.

[10] He also did a number of illustrations for the Harry N. Abrams, Inc. edition of The Hobbit, and at least one unrelated print of a samurai warrior that was purchased by Harvard University's Fogg Museum, and included in its annual undergraduate-use loan program.

"[13] Simonson then drew other DC series such as Metal Men and Hercules Unbound[14] and co-created Doctor Phosphorus with Steve Englehart.

[20] Simonson also had his first run on Thor at this time, working only as the series' artist alongside writer Len Wein.

[14] In late 1978,[21] Simonson, Howard Chaykin, Val Mayerik, and Jim Starlin formed Upstart Associates, a shared studio space on West 29th Street in New York City.

[14] In 1982, Simonson and writer Chris Claremont produced The Uncanny X-Men and The New Teen Titans intercompany crossover between the top-selling Marvel and DC titles.

In #25, the creators gave the character the Angel blue skin and metal wings in a process which would lead to his being renamed as "Archangel".

For issues #347–349, he collaborated with Arthur Adams, introducing the "New Fantastic Four" consisting of Wolverine, Spider-Man, Ghost Rider and the Hulk.

Because this idea was met with skepticism from the scientific community at the time, Simonson decided to compromise by depicting the dinosaurs with a small amount of feathers, rather than covered with them.

His other Marvel credits in the decade included co-plotting/writing the Iron Man 2020 one-shot (June 1994) and writing the Heroes Reborn version of The Avengers.

[14] In 1994 Simonson continued the adventures of the Star Slammers in a limited series as one of the founders of Malibu Comics' short-lived Bravura label.

[14] In 2002, he contributed an interview to Panel Discussions, a nonfiction book about the developing movement in sequential art and narrative literature, along with Durwin Talon, Will Eisner, Mike Mignola and Mark Schultz.

He continued to work for DC in 2006 writing Hawkgirl, with pencillers Howard Chaykin, Joe Bennett, and Renato Arlem.

[39] In 2011, Simonson had a cameo role in the live-action Thor film, appearing as one of the guests at a large Asgardian banquet.

The book shows how one silver coin paid to Judas to betray Jesus affects various characters down the centuries including Batman.

[44] It ran for twelve issues until 2017 and was followed by the six-issue mini-series Ragnarök: The Breaking of Helheim in 2019, also written and drawn by Simonson.

[45] In April 2022, Simonson and his wife Louise were reported among the more than three dozen comics creators who contributed to Operation USA's benefit anthology book, Comics for Ukraine: Sunflower Seeds, a project spearheaded by IDW Publishing Special Projects Editor Scott Dunbier, whose profits would be donated to relief efforts for Ukrainian refugees resulting from the February 2022 Russian invasion of Ukraine.