The singer announced the news on Instagram, posting a snap of herself with the words 'I'm having a baby' underneath.
As Nadine has kept quiet about her love life in recent years, the identity of her baby daddy has not been confirmed, but it was rumoured she had reunited with her ex-fiancé, American footballer Jason Bell, back in March.
The pair's relationship ended after a year's engagement in June 2011.
Nadine will be the first of her former Girls Aloud bandmates to become a mum.
Nadine suggested she wanted to continue with the girl group, tweeting: "You should know by now I had no part in any of this split business. I couldn't stop them. I had the best time & want to keep going."
The singer released her last solo album, 'Insatiable', in 2010, but it only peaked at number 47 in the UK charts.
She revealed earlier this year that she was working on new solo music.