Simon was born in Washington, D.C., the son of Dorothy Simon (nee Ligeti), a homemaker, and Bernard Simon, a former journalist and then public relations director for B'nai B'rith for 20 years. In March 1977, when Simon was still in high school, Simon's father was one of a group of over 140 people held hostage (and later released) in Washington, D.C. by former national secretary of the Nation of Islam Hamaas Abdul Khaalis in the Hanafi Siege. Simon was raised in a Jewish family with roots that originated in Eastern Europe and Hungary (his maternal grandfather had changed his surname from "Leibowitz" to "Ligeti"). He has a brother, Gary Simon, and a sister, Linda Evans, who died in 1990.

The publishers of Homicide: A Year on the Killing Streets were eager for a screen adaptation and submitted it to numerous directors but there was little interest. Simon suggested that they send the book to Baltimore native and film director Barry Levinson. Levinson's assistant Gail Mutrux enjoyed the book and both she and Levinson became attached as producers. The project became the award-winning TV series Homicide: Life on the Street (1993-1999), on which Simon worked as a writer and producer.  Simon was asked by Mutrux to write the show's pilot episode but declined, feeling he did not have the necessary expertise. He collaborated with his old college friend David Mills to write the season two premiere "Bop Gun". The episode was based on a story by executive producer Tom Fontana and featured Robin Williams in a guest starring role that garnered the actor an Emmy nomination. Simon and Mills won the WGA Award for Best Writing in a Drama for the episode. Simon also received Austin Film Festival's Outstanding Television Writer Award in 2010.  Simon left his job with the Baltimore Sun in 1995 to work full-time on Homicide: Life on the Street during the production of the show's fourth season. Simon wrote the teleplay for the season four episodes "Justice: Part 2" and "Scene of the Crime" (with Anya Epstein). For season five he was the show's story editor and continued to contribute teleplays writing the episodes "Bad Medicine" and "Wu's on First?" (again with Epstein). He was credited as a producer on the show's sixth and seventh seasons. He wrote the teleplays for parts two and three of the sixth season premiere "Blood Ties" (the latter marking his third collaboration with Epstein) and provided the story for the later sixth season episodes "Full Court Press" and "Finnegan's Wake" (with James Yoshimura). He provided the story for the seventh season episodes "Shades of Gray" (with Julie Martin), "The Same Coin" (again with Yoshimura) and "Self Defense" (with Eric Overmyer). Simon wrote the story and teleplay for the seventh season episodes "The Twenty Percent Solution" and "Sideshow: Part 2". Simon, Martin and teleplay writer T. J. English won the Humanitas Prize in the 60 minutes category for the episode "Shades of Gray". Simon was nominated for a second WGA Award for Best Writing in a Drama for his work on "Finnegan's Wake" with Yoshimura and Mills (who wrote the teleplay).  Simon has said that he thought the show was a "remarkable drama" but that it did not reflect the book. He has also said that when writing for the show he had to put his experiences of the real detectives aside as the characters became quite different, particularly in their more philosophical approach to the job. Simon said that TV must find shorthand ways of referencing anything real.

Was this a film?
Homicide: A Year on the Killing Streets