At DC Comics, he is known for co-creating the superheroes Firestorm, Power Girl, Jason Todd, and the villain Killer Croc, and for writing the Justice League of America for eight years.

Stan wasn't impressed, but Roy liked what I did, and began throwing some short assignments my way, including scripting over his plot on an early Ka-Zar [story].

He quickly went on to assignments on Iron Man, The Incredible Hulk, and both "The Inhumans" and "The Black Widow" features in the split book Amazing Adventures.

[10] At 19, Conway began scripting The Amazing Spider-Man, succeeding Stan Lee as writer of one of Marvel's flagship titles.

[15] The Punisher became a popular star of numerous comic books and has been adapted into three movies and a live action television series.

[6] In 2009, Conway reflected on writing flagship Marvel characters at a young age: Precocity is a well-known curse; most of the pressure I felt as a younger writer was self-imposed.

I wanted to be accepted by other writers and artists as an equal, which put me in some awkward situations — pretending to be more mature than I was, emotionally and professionally.

[16]In late 1972, Conway and writers Steve Englehart and Len Wein crafted a metafictional unofficial crossover spanning titles from both major comics companies.

"[17][18][19] Conway returned to DC Comics in mid-1975, beginning with three books cover-dated Nov. 1975: Hercules Unbound #1, Kong the Untamed #3, and Swamp Thing #19.

[21][22] Shortly afterward, he was chosen by Marvel and DC editors to script the historic intercompany crossover Superman vs. the Amazing Spider-Man #1, a 96-page, tabloid-sized, $2 one-shot, at a time when comic books sold for 25 cents.

[6] After leaving Marvel's editorship, he again wrote exclusively for DC for the next decade writing both major and lesser titles – from those featuring Superman, Wonder Woman, and the Legion of Super-Heroes to such books as Weird Western Tales, Atari Force and Sun Devils.

[43][44] Conway contributed ideas to the talking animal comic Captain Carrot and His Amazing Zoo Crew!, created by Thomas and Scott Shaw.

[45] Thomas and Conway were to be the co-writers of the JLA/Avengers intercompany crossover,[46] but editorial disputes between DC and Marvel caused the project's cancellation.

")[56] He also wrote the February 14–December 3, 1983, dailies of the syndicated newspaper comic strip Star Trek, based upon the 1960s TV series.

[57] Conway as well moved into screenwriting in the 1980s, starting with the animated feature Fire and Ice (1983), co-written with Roy Thomas, based on characters created by Ralph Bakshi and Frank Frazetta.

Afterwards, Conway and Thomas also worked on the script of a live-action X-Men film for production company Nelvana that wasn't produced because of distributor Orion Pictures' financial troubles and subsequent bankruptcy.

[58] Conway wrote, and later produced, such TV series as Father Dowling Mysteries, Diagnosis: Murder, Matlock, Jake and the Fatman, Hercules: The Legendary Journeys, Baywatch Nights, Pacific Blue, Silk Stalkings, Perry Mason telefilms, Law & Order, The Huntress, Law & Order: Criminal Intent, and an episode of Batman: The Animated Series ("Appointment in Crime Alley").

Because they were lower-class Irish, they were the Hispanics of their day – tolerated, but not embraced, by the larger society, and viewed with scorn by the WASP upper class.

[63] In October 2022, Conway was diagnosed with pancreatic cancer and underwent Whipple surgery to remove the tumor, resulting in several hospitalizations.