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.