Warren Leight was born to jazz trumpeter Don Leight (1923–2004), and his wife, Timmy, the second of two children. Both Warren and his older sister, Jody (born 1955), grew up with financial trouble and around clubs.

In the 1950s, his father played with jazz Musicians such as Claude Thornhill, Woody Herman and Buddy Rich. Leight's grandfather, Larry, and paternal great-grandfather, Harry Gurovitch, were also trumpet players of Russian descent. He was raised in the Sunnyside section of the borough of Queens and the Upper West Side of Manhattan.

Leight received a B.S. degree in communication from Stanford University in 1977, planning a career as a Journalist. Leight began his writing career with the 1980 horror film Mother's Day followed by the documentary Before the Nickelodeon: The Cinema of Edwin S. Porter (1982) (as the voice of "Terrible Teddy") the indie Stuck on You! (1983), and the Miramax filmThe Night We Never Met (1993), which he also directed, starring Matthew Broderick, and which earned him a nomination at the Deauville Film Festival. He wrote the screenplay for the 1996 Greg Kinnear comedy Dear God.

In the 1980s, he was the creative director/writer for a quartet of "witty" female comics known as the "High Heeled Women," which included Actress Arleen Sorkin, who performed in cabarets in New York City.

For his first stage project, Leight teamed with composer-lyricist Charles Strouse on the musical "Mayor", inspired by Ed Koch and his dealings with Leona Helmsley and Bess Myerson. It ran for 185 performances at the Top of the Gate in Greenwich Village starting on May 13, 1985. The musical transferred uptown to the Latin Quarter on October 23, 1985, running to January 5, 1986 for another 70 performances. He received a 1986 Drama Desk Award nomination for Outstanding Book.

No Foreigners Beyond This Point had its world premiere at Center Stage in Baltimore, Maryland in November 2002, directed by Tim Vasen. The play opened Off-Broadway, produced by the Ma-Yi Theater Company at The Culture Project 45 Bleecker Theatre, on September 17, 1995 in previews. Directed by Loy Arcenas, the cast included Laura Kai Chen, Ron Domingo, Wai Ching Ho, Francis Jue, Karen Tsen Lee, Abby Royle, Ean Sheehy and Henry Yuk. The play was inspired by Leight's experiences teaching English in Guangdong (Canton), China. He received a nomination for the 2006 Drama Desk Award, Play, for the Off-Broadway production.

Leight's 1998 play Side Man won him the 1999 Tony Award for Best Play and nominations for both the 1998 Drama Desk Award for Outstanding Play and the Pulitzer Prize for Drama. it starred Edie Falco and Frank Wood.

In 2001, his play Glimmer, Glimmer & Shine was produced by the Mark Taper Forum in Los Angeles. It was produced Off-Broadway by the Manhattan Theatre Club from May 24, 2001 to July 8, 2001. John Spencer appeared in both productions, directed by Evan Yionoulis.

Leight ventured into television as a freelance Writer for 100 Centre Street in 2002. On a suggestion from Playwright Theresa Rebeck, Law & Order: Criminal Intent executive Producer René Balcer hired Leight to join the staff of the series in its second season as a writer/producer. His colleagues included a reference to Leight's play "Side Man"; in a third-season episode, "Shrink-Wrapped"; a bickering couple argues about the motivations of the married couple in the play. Upon a recommendation from Balcer, Leight was named the show's executive Producer and head Writer in 2006 when Balcer left the show at the end of the fifth season.

His play James and Annie premiered at the Ensemble Theatre of Cincinnati in March 2003. The play involves an "interracial love affair".

In 2008, he left Criminal Intent after its seventh season to be the showrunner for HBO's series In Treatment, a year after CI moved to cable. In July 2009, it was announced that Leight had joined FX's new drama Lights Out.

On April 11, 2011, Variety reported that Leight would serve as showrunner for Law & Order: Special Victims Unit starting with the thirteenth season. Prior to Leight joining SVU, he wrote one of the final episodes of Law & Order: Criminal Intent, the 10th season episode "Trophy Wine", which was the only episode of the season not to be inspired by a real life, true event. Before production on the 13th season of Law & Order: SVU, NBC President, Bob Greenblatt sought Leight to "reset the tone" of the show from its prior seasons, while having the storylines "still be compelling but a little more grounded".

In October 2012, Leight said of the Future of the Law & Order franchise – which currently consists of just Law & Order: SVU – "(Dick Wolf and I) sometimes talk in general terms of where (the franchise) could go. I'm curious to see if there's another iteration somewhere down the line," he says. "We try hard to maintain a certain level of quality which I think is why the shows sustained in reruns so well. And I'd like to believe there's room for another generation in some way."

Prior to SVU being renewed for a 14th season, Leight said to TV Guide, "I don't want it to be a victory lap, I want it to be 14 years down, seven to go, as opposed to 14 years down and it's been a good run." Ratings "roller-coastered" in season 13, from its lead-in at the time, Rock Center with Brian Williams with competition from CSI: Crime Scene Investigation on CBS and Revenge on ABC. "I get so tired of people saying that the show is down from Meloni," Leight says. "From the point of view of scripted hour-longs, we're performing very strongly for NBC. Would we perform differently for a different network? Probably. Or with a different lead-in? Probably."

In May 2016, Leight ended his reign at SVU to develop new television ideas for Sony.