Don Heck's professional career began in 1949 when he got a job in the production department of Harvey Comics. Heck did his first comic book illustration through Quality and Hillman however. he eventually worked for Comic Media for two years, working on their line of horror and war titles. In 1954, Heck joined Charlton Comics, where he did 'Captain Gallant of the Foreign Legion'. He eventually became a mainstay at Altas/Marvel, where he started out illustrating 'Torpedo Taylor' in Navy Combat and 'Cliff Mason' in Jungle Tales and Jann of the Jungle.
After a brief interlude drawing airplane models, Heck returned to work on the comic books Journey in Mystery and Tales of Suspense. Heck's first super-hero assignment was on the first 'Iron Man' story, which appeared in Tales of Suspense in 1963. Heck also did work on early stories of 'Thor' and 'Giant Man'. But he is probably best remembered for his long, first run on 'The Avengers', that started in 1964. During his time at Marvel, he also contributed to the art on 'Spider-Man', 'X-Men' and many more.
In the mid-1960s, Heck additionally worked for Western Publishing on the 'Man from U.N.C.L.E.' comic book and assisted Sy Barry and Joe Giella on the 'The Phantom' newspaper strip. In 1971, Don Heck was considered the best renderer of attractive women in comics by Jack Kirby, who suggested him to DC as an artist for 'Batgirl'.