The singer, real name Melanie Chisholm, gave birth to Scarlet Starr on Sunday morning.
Both mother and baby, weighing 8lb 3oz, "are doing fine", according to her spokeswoman.
The baby's father is Thomas Starr, her partner of six years.
A message on her website said: "Melanie C gave birth to a beautiful little girl at 4.10pm on Sunday February 22. Both mum and baby are doing well."
Sporty Spice, as she was known in the Spice Girls, is the last of the girl group to become a mother.
Victoria Beckham has three sons Brooklyn, Romeo and Cruz; Emma Bunton has a son called Beau; Melanie Brown has two daughter Phoenix Chi and Angel, while Geri Halliwell has a daughter Bluebell.
In an interview last year before she announced her pregnancy, Mel C said: "I love kids and one of the best bits about touring with the Spice Girls this time round was getting to know everyone's babies. I'm sure that babies will be part of my future."
Mel C had arguably the most successful solo career of any of the Spice Girls.
She released four albums, and recorded two number ones in 2000 with I Turn To You and Never Be the Same Again.
Although she expected to record a fifth solo album, the singer will take time out of her career to care for her daughter.
