The singer, 33, and her fiancé Matt Rutler welcomed their first child together on Saturday 16 August, says Us Weekly.
According to the website, she gave birth via a C-section at Cedars-Sinai Medical Centre in Los Angeles.
The 'Genie In A Bottle' singer confirmed she was expecting a baby with Matt in April, just months after getting engaged in January.
Despite keeping mum about her pregnancy at first - despite persistent rumours - Christina proved she was pregnant and proud when she posed completely naked while heavily pregnant this month.
The baby girl will be a younger sister to Christina's first child, 6-year-old Max, from her first marriage to Jordan Bratman.
Christina appeared to work right up until her due date as she posted a photo of herself in the studio last week, along with the caption: "Baby girl getting first listen to what mama's been creating in the studio."
A big congratulations to the happy couple on their new arrival!
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See the official video to Christina Aguilera's 'Your Body':