Nicole Kidman gave birth on a Monday to a baby girl named Sunday.
The baby is the first for Kidman and country singer Keith Urban, who married in June 2006.
Paul Freundlich, a publicist for Urban, said: "Nicole and Keith Urban are delighted to announce that Nicole Kidman gave birth to a baby girl on Monday morning, 7 July, 2008, in the United States. Sunday Rose Kidman Urban weighed 6 pounds, 7 1/2 ounces. Husband Keith was by Nicole's side and mother and baby are very well."
Urban posted a message on his website that said: "Earlier this morning Nic gave birth to our beautiful baby girl, Sunday Rose Kidman Urban. We want to thank everybody that has kept us in their thoughts and prayers. We feel very blessed and grateful that we can share this joy with all of you today."
Kidman has two children, Isabella and Connor, from her marriage to Tom Cruise.
Kidman recently told Vanity Fair that she had a miscarriage early on in her relationship with Cruise, leading them to adopt.
Cruise filed for divorce in February 2001 after 10 years of marriage, citing irreconcilable differences. The divorce was finalised later that year.
Kidman, 41, won an Oscar for her role in the 2002 film The Hours.
During a concert on Saturday in Nashville, Urban said, "I'm going to dedicate a song to my very, very, very, very, very pregnant wife" before singing his hit, Better Half.
Urban, 40, won a Grammy in 2006 for best male country vocal.
The couple, who were both raised in Australia, have a home in Nashville.
In a recent radio interview in Nashville, Kidman revealed that Urban had been getting hands-on in preparation for the birth by attending Lamaze lessons, saying, "He doesn't know the name (of the classes), but he has been very good at it!"