Greenberger was born in Brooklyn, New York, the son of Edwin L. and Joan Greenberger. He attended Binghamton University, where he wrote and edited for the college newspaper, Pipe Dream, and also interned at the Binghamton Sun-Bulletin.

Following his graduation, he worked as an editor for Comics Scene and Starlog Press until 1984, when he joined DC Comics as an assistant editor. Greenberger was taken on to assist Len Wein and Marv Wolfman by the then DC Vice President/Executive Editor Dick Giordano. The company was then rationalising its output with the major comic book crossover Crisis on Infinite Earths and the guidebook Who's Who in the DC Universe. Based on his work during this period, Greennberger was promoted to editor the following year, being assigned the titles Star Trek, Suicide Squad and Doom Patrol. Under his editorship the DC Comics adaptation of The Motion Picture was released, and Greenberger became involved with the Trek franchise, authoring a number of novels and stories set within the Star Trek universe. He worked at DC until 2000, having risen to the position of Manager-Editorial Operations. During this time, he worked on such titles as Warlord, Lois Lane, Action Comics Weekly, Time Masters, Secret Origins, The Hacker Files and others.

His editorial work on the Star Trek comics led to numerous contributions to the franchise's novel series. In 2001, he and novel editor John J. Ordover developed the seven-book crossover miniseries Gateways. Greenberger wrote the third novel of the series, as well as the concluding novella.

Greenberger left DC in 2000 and joined the online company Gist Communications. This break with the comics industry lasted until 2001, when he joined Marvel Comics as Director-Publishing Operations. Greenberger was hired to work under Joe Quesada, but was let go during a tumultuous reorganization overseen by Bill Jemas. He soon rejoined DC Comics as a Senior Editor for Collected Editions, but was let go from his position in 2006 after a reorganisation at DC and also after a publishing error which saw copies of the Golden Age hawkman Archives printed with pages in the incorrect order. His firing was criticised by comic book writers Peter David and Christopher Priest. Greenberger found work as a freelance writer and editor, working for such companies as Weekly World News, Platinum Studios, scifi.com, Famous Monsters of Filmland, and ComicMix.com, as well as both DC and Marvel. From June 2006 to August 2007, he also served as Managing Editor at Weekly World News.

Politics

Greenberger became involved in local politics in his home of Fairfield, Connecticut beginning in 1999, initially as member of the Parking Authority. He served as a Representative to Fairfield’s Representative Town Meeting from 2005 to 2009, losing a bid for a third two-year term in 2009.

Greenberger is a member of the Science Fiction Writers of America, where he has served as a judge for the Nebula Awards, and of the International Association of Media Tie-In Writers.

He was married to Deborah Upton in 1980. They are the parents to Kathleen Michelle (born 1986) and Robert Edward Jr. (born 1988, died 2008).

Novels

• Doomsday World (The Next Generation (TNG), with Peter David, Carmen Carter, and Michael Jan Friedman, 1991)
• The Disinherited (Star Trek, with Peter David and Michael Jan Friedman, 1992)
• The Romulan Stratagem (TNG, 1995)
• Wrath of the Prophets (Deep Space Nine, with Peter David and Michael Jan Friedman, 1997)
• Time Station Berlin (as David Evans, 1997)
• Doors Into Chaos (TNG, 2001)
• A Time to Love (TNG, 2004)
• A Time to Hate (TNG, 2004)
• Flesh & Blood (Predator, with Michael Jan Friedman, 2007)
• Hellboy II: The Golden Army (film novelization, 2008)
• Batman: Arctic Attack (2009)
• Femme Fatales (Iron Man, 2009)
• Batman: Hunt the Dark Knight (2010)

Short stories and novellas

• "Memories of Erin" (1997)
• "Solo" (1998)
• "Hour of Fire" (Star Trek, 2000)
• "The Other Side" (TNG, 2001)
• Past Life (Starfleet Corps of Engineers (SCE), 2002)
• "A Matter of Faith" (2002)
• Buying Time (SCE, 2003)
• "Lefler's Logs" (New Frontier, 2003)
• "A Song Well Sung" (Star Trek, 2004)
• "Command Code" (Voyager, 2005)
• "The Landing Party" (Star Trek, 2006)
• "Things That Aren't" (with Michael A. Burstein, 2007)
• "Rain of Tears" (Zorro, 2007)
• Troubleshooting (SCE, 2007)
• A Weary Life (TNG, 2007)

Other

• Q's Guide to the Continuum (Star Trek reference book, with Michael Jan Friedman, 1998)
• The DC Comics Encyclopedia (with Phil Jimenez, Scott Beatty and Dan Wallace, 2004)
• The Essential Batman Encyclopedia (2008)
• Batman Vault (with Matthew K. Manning, 2009)
• The Essential Superman Encyclopedia (with Martin Pasko, due mid-2010 from Del Rey Books)