The singer found out she was expecting after taking a pregnancy test in a public toilet during a trip to Asda with her husband. Her baby is due in late December.
She told The Sun: "I went in and did it while he was getting all the food. I came out and went 'Yep – I'm pregnant!' It wasn't planned."
A spokesperson for the singer said: "Sam and her family are absolutely delighted and cannot wait to welcome their new addition to the family."
Sam has already lined up X Factor mentor Sharon Osbourne as a celeb godparent. Sharon tweeted: "@SamBaileyREAL I would be honoured to be your baby's Godmother!"