Around this time, Gruenwald also began editing various titles within the 'Avengers family' of books such as Avengers and Thor. The series also introduced Crossfire and the Death-Throws.

Perhaps Gruenwald's first break-out role was writing and pencilling the first Hawkeye series: a series which acted as a percursor of sorts to West Coast Avengers and saw Hawkeye meet and elope with Mockingbird. Unsurprisingly, shortly afterwards he began writing and compiling the first series of the Official Handbook to the Marvel Universe which greatly expanded on the profiles included in Contest of Champions - giving every character at least half a page for a profile. Again, against all odds, Gruenwald manages to briefly profile characters as obscure as Powerhouse, Star-Dancer and Tagak alongside the likes of Spider-Man and Captain America. Despite clocking in at barely 3 pages each issue, Gruenwald managed to fit in a surprising amount of detail such as first appearances, powers and current whereabouts of the characters. The final pages of each issue of Contest of Champions presented a crude and brief catalogue of Marvel's superheroes entirely written and compiled by Gruenwald. Even in the modern day, the template is still used by Marvel with crossover limited series such as Civil War, Secret Invasion and Fear Itself. The basic premise and practice of the storyline and series became a staple of Marvel comics and was followed up by the likes of Secret Wars and Infinity Gauntlet. Entitled Contest of Champions, the story saw all of Earth's heroes being abducted by a cosmic being and forced to participate in a competition.

Gruenwald also wrote Marvel's first limited series which was also their first attempt at a crossover storyline.

Some noteworthy early work includes the Pegasus Project, Eternals Saga and Nights of Wundagore story arcs. Despite his early work not being quite as well known as some of his later projects, he created several characters of particular note such as Screaming Mimi, Quasar and the Shroud. Mark Gruenwald's early work at Marvel ranged from significant runs on Spider-Woman and The Thing to various fill-in issues of titles such as The Avengers and Thor.

Squadron supreme by mark gruenwald