The pop star announced the news on Monday (24Feb14) in a post on her Twitter.com page, revealing she is expecting a baby with her long-term boyfriend Justin Scott, a former member of U.K. boyband Triple 8.
She writes, "Justin and I are so happy to let you all know we are having a baby!!! Couldn't wait to share our lovely news with you all."
Walsh's announcement comes just days after her former bandmate Nadine Coyle welcomed a daughter.
Coyle became a first-time mother on 10 February (14).