Larry Rudolph, who helped Spears secure her first recording contract, said the star's "intention to officially retire" had prompted him to resign.
The move comes two weeks after Spears told an LA judge that she had been forced to perform against her will.
She is currently seeking to end a conservatorship that has governed her life and finances since 2008.
Rudolph announced his intention to resign in a letter to the star's father, Jamie Spears, and co-conservator Jodi Montgomery.
