[5][6] A four-time Eisner Award winner and five-time Wizard Fan Awards winner, Loeb's comic book work, which has appeared on the New York Times Best Seller list, includes work on many major characters, including Spider-Man, Batman, Superman, Hulk, Captain America, Cable, Iron Man, Daredevil, Supergirl, the Avengers, and Buffy the Vampire Slayer, much of which he has produced in collaboration with artist Tim Sale.

[9] His stepfather was a vice-president at Brandeis University, where Jeph met one of his mentors and greatest influences in comic book writing, the writer Elliot Maggin.

He signed a three-year contract, and although producers Miles Millar and Alfred Gough offered to keep him on for future seasons, Loeb left to care for his son, who had cancer (See Comics career below).

Leaving Lost, Loeb went on to become Co-Executive Producer and writer on the NBC drama Heroes, which his colleague Tim Kring had created.

[22] Loeb himself was also presented with a belated 2005 Jules Verne Award for Best Writing for his work on Smallville, which he had not previously been given because his trip to the Festival that year had been cancelled due to his son's ill health.

[23] On November 2, 2008, Daily Variety reported that Loeb and fellow Heroes co-executive producer, Jesse Alexander, were no longer employed on the series.

[33] At Marvel Comics, Loeb worked on the "Age of Apocalypse" crossover storyline in 1995[34] and co-created the character X-Man with artist Steve Skroce.

[36] He and Tim Sale crafted several limited series for Marvel including Daredevil: Yellow,[37] Spider-Man: Blue,[38] and Hulk: Gray.

At the end of 2002, Loeb teamed with artist Jim Lee to create the year-long story arc "Batman: Hush",[42] which spawned three lines of toys, posters and calendars, and sat at the #1 spot for eleven of the twelve months it was in publication.

[46] In 2006, Loeb chose his hometown of Stamford, Connecticut, to be subject to superhero destruction in the first issue of the 2006–2007 Marvel miniseries Civil War, the central title of the crossover storyline of the same name.

1 in sales for April 2007,[52] and the fifth and final issue, dated July 4, 2007, was the "Funeral for Captain America", which was covered by the Associated Press and The Washington Post.

His work on The Ultimates 3 in 2007, with artist Joe Madureira, was panned by critics for its use of transgressive sexual and violent content for shock value "without the political relevance or epic pacing of the first two volumes."

In 2008, Loeb returned to the Ultimate Universe with artist David Finch for the critically reviled five-issue miniseries Ultimatum.

Described in a 2015 Vulture retrospective as "one of the biggest creative disasters in comics history", Ultimatum's gratuitous murder scenes permanently damaged sales across the entire Ultimate Universe and in the long run brought about its cancellation.

"Over the course of just five issues, 34 different heroes and villains were murdered, often by gruesome means: Doctor Strange was squeezed until his head exploded; Magneto was decapitated; the Blob ate the Wasp and, while holding her half-devoured corpse, belched out, 'Tastes like chicken'; and so on."

[55] Loeb shares his writing studio, The Empath Magic Tree House, with Geoff Johns and Allan Heinberg.

[63][64][65] During the #SaveDaredevilCon panel for Comic-Con@Home in July 2020, Peter Shinkoda, a Canadian actor of Japanese descent who played recurring villain Nobu Yoshioka on Daredevil, suggested that Loeb forced the show's writers to drop proposed storylines fleshing out Nobu and fellow recurring villain Madame Gao.

"[66][67][68] Shinkoda also claimed that he and Gao's actress Wai Ching Ho were not invited to the season 2 premiere of Daredevil and received less payment than the extras.

Co-star Tommy Walker said that Daredevil and Defenders showrunner Doug Petrie had previously pitched a multiracial Asian American version of Iron Fist to Marvel Television in early development, but was rejected by Loeb.

[93] IGN's Jesse Schedeen gave the series' final issue a scathing review, saying, "Ultimatum is one of the worst comics I have ever read," and called it "the ultimate nightmare.

"[94] Points of criticism among these reviews included the level of graphic violence, which included cannibalism, and the notion that the series was sold on the basis of its shock value,[95] with some reviewers singling out Loeb's dialogue, characterization and storytelling,[76][96] others asserting the story's lack of originality,[97][98] or opining that the series would've been better suited to someone who had previously been more involved with the Ultimate line, such as Brian Michael Bendis or Mark Millar.