Broome began his career as a writer of a dozen published science-fiction stories. He switched to writing comic books for his friend and former agent, DC editor Julius Schwartz.http://www.comic-con.org/cci/cci_finger.shtml According to writer Mark Evanier, Broome's work for DC appeared from 1946 to 1970, and included the Green Lantern and Flash series in the late 1950s and 1960s period known to historians and fans as the Silver Age of Comic Books, as well as several Justice Society of America stories during that time.

Broome created many DC characters and institutions, including the 1940s Detective Chimp, Per Degaton, the Atomic Knights, the Silver Age Flash Rogues Gallery of supervillains, the Green Lantern Guardians of the Universe, and the Elongated Man.

According to his own account, Broome loved to travel the world and wrote for money. Gradually losing his enthusiasm for comic books, he diminished his production of scripts and retired from comic book scripting entirely in 1970. Broome spent many years teaching English in Tokyo, Japan. He returned to the United States in 1998, attending his first comic book convention, the San Diego ComicCon.

Broome died in Thailand.

Broome received a 1964 Alley Award for Best Short Story: "Doorway to the Unknown!" in Flash #148, with artist Carmine Infantino. He posthumously received the Bill Finger Award for Excellence in Comic Book Writing in 2009.

An homage to Broome and artist Gil Kane appears in the novel In Darkest Night, which is set in the universe of the Justice League animated series. In the novel, a place in Coast City is named the "Kane/Broome Institute for Space Studies".