The 31-year-old Spice Girls singer gave birth to a son, Beau, at London's Portland Hospital on Friday, a spokesman said.
He is the first child for Bunton and boyfriend Jade Jones.
"He is absolutely brilliant and both baby and Emma are doing fine," Jones said in a statement. "In fact, Emma is tucking into some flapjacks and Coca-Cola as we speak. We are both absolutely delighted and can't wait to take Beau home."
The Spice Girls -- Bunton, Victoria Beckham, Melanie Chisholm, Geri Halliwell and Melanie Brown -- had a string of global hits before splitting in 2001. In June they announced they were reuniting for a tour that will begin later this year.