The Irish singer's wife Georgina Ahern welcomed baby daughter Gia on Wednesday morning (23Oct13).
Taking to Twitter.com to announce the happy news, Byrne writes, "Our beautiful Baby Girl Gia... Was born today at 1030am. She is absolutely beautiful, just like her mommy! We are thrilled."
The couple is already parents to six-year-old twin boys Rocco and Jay.
After hearing the news, Byrne's former bandmate Shane Filan sent his well wishes, tweeting, "Huge congrats (sic) to (Georgina) & nickybyrneoffic on the arrival of their little princess Gia. Amazing news!! Can't wait to see her!"