People.com said the "Pulp Fiction" and "Kill Bill" star's baby was born Sunday.
"Mom and baby are doing well," Thurman's representative told the celebrity news magazine.
No other details regarding the birth such as where it took place and what the baby's name is were immediately released.
The actress is engaged to financier Arpad Busson and has two older children with her ex-husband, actor Ethan Hawke.
Busson, 49, has two children with his ex-fiancee, supermodel Elle MacPherson.
Thurman and Busson began dating in 2007.