Weil was trained as an actress and dancer but soon demonstrated a songwriting ability that led to her collaboration with Barry Mann whom she would marry in August 1961.. The couple has one daughter, Dr Jenn Berman, AKA "Dr. Jenn". Weil became one of the Brill Building songwriters of the 1960s, and one of the most important writers during the emergence of rock and roll.
She and her husband went on to create songs for numerous contemporary artists, winning a number of Grammy Awards and Academy Award nominations for their compositions for film. As their Rock and Roll Hall of Fame biography put it, in part: "Mann and Weil ... [works went from] epic ballads (“On Broadway,” “You’ve Lost That Lovin’ Feelin’”) to outright rockers (“Kicks,” “We’ve Gotta Get Out of This Place”) [and they also] placed an emphasis on meaningful lyrics in their songwriting. With Weil writing the words and Mann the music, they came up with a number of songs that addressed such serious subjects as racial and economic divides[,] “Uptown,” ... and the difficult reality of making it in the big city (“On Broadway,” ...). “Only in America” ... tackled segregation and racism, making it rather too controversial for the Drifters, who were the intended artists. “We Gotta Get Out of This Place” ... became an anthem for [the] Vietnam soldier, antiwar protesters, and young people who viewed it as an anthem of greater opportunities."
In 1987, she was inducted with her husband, Mann, into the Songwriters Hall of Fame. In 2004, Mann and Weil’s They Wrote That?, a musical revue based on their songs, opened in New York. In it, Mann sang and Weil related stories about the songs and their personal history.
Weil and Mann were named among the 2010 recipients of Ahmet Ertegun Award from the Rock and Roll Hall of Fame. At the ceremony at the Waldorf-Astoria, which was telecast on the Fuse TV cable network, songwriter Carole King inducted Mann and Weil and other songwriting colleagues from the 1950s and early 1960s, including Ellie Greenwich (posthumously) and Jeff Barry, Otis Blackwell (posthumously), Mort Shuman, and Jesse Stone (posthumously). "From the bottom of my heart and with the greatest humility," Ms. Weil said in her acceptance. "I thought you guys would never ask." Eric Burdon of The Animals and Ronnie Spector of The Ronettes performed at the ceremony. In 2011 Mann and Weil received the Johnny Mercer Award -- the highest honor from the Songwriters Hall of Fame. 
Songs written by Barry Mann and Cynthia Weil 
- "A World of Our Own" - Closing theme song from Return to the Blue Lagoon - Surface
- "Black Butterfly" - Deniece Williams
- "Blame It on the Bossa Nova" – Eydie Gormé
- "Bless You" - Tony Orlando
- "Christmas Vacation" - Title song for the movie of the same name
- "Don't Know Much" – Aaron Neville & Linda Ronstadt (also, earlier, Bill Medley and Bette Midler)
- "He's Sure the Boy I Love" – The Crystals
- "Heart" - Kenny Chandler
- "Here You Come Again" – Dolly Parton
- "Hungry" - Paul Revere & the Raiders
- "I Just Can't Help Believing" – B. J. Thomas, Elvis Presley
- "I'm Gonna Be Strong" – Gene Pitney and covered by Cyndi Lauper
- "I Will Come to You" - Hanson
- "Just a Little Lovin' (Early in the Morning)" - Dusty Springfield, Carmen McRae, Barbra Streisand, Billy Eckstine, Bobby Vinton
- "Just Once" - James Ingram with Quincy Jones
- "Kicks" – Paul Revere & the Raiders
- "Let Me In" (Rick Derringer/Cynthia Weil) - Derringer
- "Looking Through the Eyes of Love" - Gene Pitney, Marlena Shaw
- "Love Doesn't Ask Why" - co-written with Phil Galdston. Recorded by Celine Dion.
- "Love is Only Sleeping" - The Monkees
- "Magic Town" – The Vogues
- "Make Your Own Kind of Music" – "Mama" Cass Elliot
- "Never Gonna Let You Go" - Sérgio Mendes and Dionne Warwick
- "None of Us Are Free" (Mann, Weil, Brenda Russell) - Ray Charles, Lynyrd Skynyrd, Solomon Burke
- "On Broadway" – The Drifters and later George Benson
- "Only in America" – Jay and the Americans
- "Remember" - Song from Movie Troy - Covered by Josh Groban
- "Running with the Night" (Lionel Richie & Cynthia Weil) - Lionel Richie
- "Shades of Gray" - The Monkees
- "Shape of Things to Come" – Max Frost and the Troopers
- "Somewhere Out There" - co-written with James Horner for the film An American Tail, won a pair of Grammys in 1987, including Song of the Year; recording by Ronstadt and Ingram.
- "Uptown" – The Crystals
- "Walking in the Rain" - The Ronettes
- "We Gotta Get out of This Place" – The Animals
- "Where Have You Been All My Life"- The Beatles, recorded live 31 December 1962 at the Star Club, Hamburg, Germany; also Roy Clark, 1978, Labor of Love album
- "(You're My) Soul and Inspiration" – The Righteous Brothers and later Donny & Marie Osmond
- "You've Lost That Lovin' Feelin'" co-written with Phil Spector - The Righteous Brothers and later numerous other artists including Dionne Warwick, Hall & Oates, and a Roberta Flack-Donny Hathaway duet. As of 2010[update], the Righteous Brothers' rendition was radio’s most-played song of all time, with 14 million airplays to date.
- Biography Rock and Roll Hall of Fame. Retrieved 2010-03-16.
- "Congratulations to the 2010 Rock and Roll Hall of Fame Inductees!". Retrieved 2009-12-15.
- "Rock Hall welcomes Genesis, ABBA, Iggy" by David Bauder, Associated Press via torontosun.com, March 16, 2010 11:34am. Retrieved 2010-03-16.
- "Rock and Roll Hall of Fame Inducts New Members" by Jon Pareles, The New York Times, March 15, 2010 (March 16, 2010 p. A16 NY ed.). Retrieved 2010-03-16.
- "Garth Brooks, Billy Joel perform together during Songwriters Hall of Fame ceremony". Soundspike.com. 2011-06-17. Retrieved 2012-04-16.
- Beatles Lyric, Jiri Wagner © 1999 - 2010 at boskowan.com. Retrieved 2010-03-16.
- Audio interview with Cynthia Weil and Barry Mann on the Sodajerker on Songwriting podcast
- Cynthia Weil biography at Allmusic website