Born in Attalla, Alabama, Kelly's family moved to Detroit, Michigan when Kelly was a child. Like many children growing up in "Motown," Kelly wanted a career in music.
In 1961, she joined the Motown singing group The Velvelettes. (She wasn't part of the group when the band had a hit with "Needle in a Haystack") in 1965.
Around this time, Kelly was recruited by Motown president Berry Gordy to replace departed Martha and the Vandellas member Annette Beard as a member of the group led by Martha Reeves and featuring Rosalind Ashford.
The name Vandellas came from a street near Martha Reeves - Van Dyke Street in Detroit - and the Della part honored Della Reese, Reeves' favorite singer and a Detroit native herself.
Betty Kelly joined what became the most famed lineup of the Vandellas, recording "Live Wire," The group then recorded their "signature songs," including "Dancing in the Street," "Nowhere to Run" and "Jimmy Mack." (Kelly was often mistaken for being an original member of the group despite the fact that Beard had sung on the group's earlier singles, often lip-synched by Kelly when the group performed on TV.)
"Dancing in the Street" was inducted to the Grammy Hall of Fame in 1999. In 1993, the women were awarded the Pioneer Award at the Rhythm & Blues Foundation. Members of the group were inducted to the Rock & Roll Hall of Fame in 1995, becoming just the second all-female group to be inducted.
In 2005, Martha & The Vandellas were inducted into the Michigan Rock and Roll Legends Hall of Fame. "Dancing In The Street" was voted a Legendary Michigan Song in 2008.
In 2004, Rolling Stone ranked Martha and the Vandellas #96 on their list of the 100 greatest artists of all time.
During the group's later years, Kelly performed some lead singing parts during the group's performances alongside Reeves, which led to infighting between the two- often during performances on stage. By 1967, Kelly was kicked out of the group after being late to several performances and was quickly replaced by Martha's younger sister Lois Reeves with the group's name changed to Martha Reeves and the Vandellas.