Bittan has played on several dozen albums, not only for Springsteen but also David Bowie, Jackson Browne, Tracy Chapman, Chicago, Catie Curtis, Dire Straits, Peter Gabriel, Ian Hunter, Meat Loaf, Stevie Nicks, Bob Seger, Celine Dion, Patty Smyth, Jim Steinman, and Bonnie Tyler.

Bittan was born in Rockaway Beach, Queens, New York City. He is a long-time member of Bruce Springsteen's E Street Band, and has performed on the majority of Springsteen's albums, beginning with Born to Run in 1975. In Springsteen's band introductions, Bittan's "Professor" moniker is supposedly (but falsely) given to his being the only group member with a high school diploma. Bittan provided background vocals for most of the songs on Born to Run, along with Steven Van Zandt. His voice is also featured slightly on the vocal weaving in "Out in the Street". However, from the Born in the U.S.A. Tour on, his voice was no longer used. When Springsteen decided to break his cooperation with the E Street Band in 1989, Roy Bittan was the one member kept on, both in studio and on the "Other Band" Tour.

With the E Street Band, Bittan uses a Yamaha grand piano, preferring the bright sound to cut through the group's sound compared with other acoustic models. He has also been known to use Yamaha, Korg and Kurzweil keyboards as part of his live rig. His riffs and melody lines have become signatures for the Springsteen sound. Roy is an avid accordion player, which was a skill he seldom used with the E Street Band until playing "American Land" as the closing number on the 2007-2008 Magic Tour and then later taking the instrument's part on "4th of July, Asbury Park (Sandy)" after the passing of bandmate Danny Federici.

Bittan played piano nearly exclusively on Meat Loaf's 1977 hit album Bat out of Hell. Composer Jim Steinman wanted Bittan for the album due to his love for Springsteen's early work, particularly on Born to Run. Since then, Bittan has regularly and nearly exclusively collaborated with Steinman, appearing on three more Meat Loaf albums (most notably Bat out of Hell II: Back into Hell), Steinman's solo album Bad for Good, an Air Supply single, a Barbra Streisand single, an album by Pandora's Box, Total Eclipse of the Heart, and others.

Bittan played with Fire Inc, a Wagnerian rock band that released two songs for the rock and roll film Streets of Fire in 1984. The two songs never had any real commercial success. In 1989 Jim Steinman put together another group called Pandora's Box in which he included eight of the members from Fire Inc.

Bittan is on the Dire Straits album Making Movies. Mark Knopfler's decision to have the keyboardist on the album's lineup was reportedly influenced by his affection for "Because the Night", a keyboard-driven hit song cowritten by Springsteen and Patti Smith.[citation needed]

Bittan played on the second solo album from Peter Gabriel, appearing on several tracks including "On the Air", "Mother of Violence, "D.I.Y." and "White Shadow".

Bittan played on two David Bowie albums, Station to Station (1976) and Scary Monsters (and Super Creeps) (1980).

Bittan played an important part in the sound Stevie Nicks created for her solo debut away from Fleetwood Mac, 1981's Bella Donna. About the time that the album reached number one in the United States, Roy also went on a short tour with Nicks along with some of the other top musicians of the day: Benmont Tench on organ, Bob Glaub on bass, Waddy Wachtel on guitar, Russ Kunkel on drums, and Bobbeye Hall on percussion. Bittan also played on Nicks' second solo album The Wild Heart and has continued to play with her sporadically.

Bittan played piano on the track entitled "Heart And Soul" on Shwayze and Cisco Adler's second album, Let It Beat.