He gained worldwide fame for starring as NYPD Detective Lennie Briscoe on the NBC legal drama Law & Order from 1992 to 2004.

[6] His mother, a native of Luzerne County, Pennsylvania, was a Roman Catholic of Polish-Lithuanian descent, and Orbach was raised in her faith (a religious background later replicated in his character on Law & Order).

[7][8][9] The Orbach family moved frequently during his childhood, living in Mount Vernon, New York; Wilkes-Barre, Nanticoke, and Scranton, Pennsylvania; Springfield, Massachusetts; and Waukegan, Illinois.

His first major role was El Gallo in the original 1960 cast of the decades-running hit The Fantasticks, and Orbach became the first to perform the show's signature song and pop standard "Try To Remember".

[12] He also starred in The Threepenny Opera; Carnival!, the musical version of the movie Lili (his Broadway debut); in revivals of Annie Get Your Gun and Guys and Dolls (as Sky Masterson, receiving a Tony Award nomination for Best Featured Actor in a Musical); Promises, Promises (as Chuck Baxter, winning a Tony Award for Best Actor in a Musical); the original productions of Chicago (as Billy Flynn, receiving another Tony Award nomination); 42nd Street; and a revival of The Cradle Will Rock.

Prominent roles included tough, corrupt NYPD narcotics detective Gus Levy in Sidney Lumet's Prince of the City; he was the 1981 runner-up for the NSFC Best Supporting Actor award.

He also portrayed gangsters in both the action-thriller F/X and the Woody Allen drama Crimes and Misdemeanors (the latter of which also featured his future Law & Order co-star Sam Waterston).

In 1991, Orbach starred in Steven Seagal's action film Out for Justice as police captain Ronnie Donziger, and starred in Disney's Oscar-winning animated musical Beauty and the Beast as the voice (both singing and speaking) of the French-accented candelabrum Lumière, which he played "halfway between Maurice Chevalier and Pepé Le Pew".

[3] At the 64th Academy Awards, Orbach performed a live-action stage rendition of the Oscar-nominated song, "Be Our Guest", that he sang in Beauty and the Beast.

[13][14] He later reprised his voice role of Lumière for the film's direct-to-video sequels, multiple episodes of House of Mouse, and the previously-deleted song ("Human Again") that was added to the Beauty and the Beast 2002 IMAX re-release.

[15][16] In 1992, Orbach joined the main cast of Law & Order during its third season as the world-weary, wisecracking NYPD homicide detective Lennie Briscoe.

[5] Orbach's portrayal of Briscoe was based on his similar role from Prince of the City years before, which Law & Order creator Dick Wolf had personally suggested to him at the time of his casting.

[3] Orbach starred on Law & Order for 11+1⁄2 seasons, ultimately becoming the third longest-serving main cast member (behind S. Epatha Merkerson and Sam Waterston) in the show's 20-year-run history, as well as one of its most popular.

Orbach himself was nominated for a 2000 Primetime Emmy Award for Outstanding Lead Actor in a Drama Series (losing to James Gandolfini for The Sopranos).

[23] Orbach was signed to continue in the role of Lennie Briscoe on the new spin-off Law & Order: Trial by Jury, which gave him a lighter schedule than the original series, but he was only featured in the first two episodes, both of which aired after his death.

[3] The day after Orbach's death, the marquees on Broadway were dimmed in mourning, one of the highest honors of the American theatre world,[3] while NBC re-aired the Law & Order episode "C.O.D."