(5 August 2003 - present) (3 children)
1. Rocco Bertie (20 April 2007) Twin
2. Jay Nicky (20 April 2007) Twin
3. Gia Byrne (23 October 2013)
Byrne married his teenage sweetheart Georgina Ahern, whom he met when they were about 12 years old. The two were married on 5 August 2003 at the Wicklow Register Office, Wicklow, County Wicklow. The civil ceremony was followed by a church blessing on 9 August at the Roman Catholic Church of St Pierre et St Paul in Gallardon, Eure-et-Loir, France and a reception at the nearby 16th century Château d'Esclimont. Georgina gave birth to fraternal twin sons, Jay and Rocco, on 20 April 2007, born eight weeks prematurely. The children were baptised on 15 July 2007 in the Saint Sylvester Roman Catholic Church in Malahide, County Dublin. On 29 April 2013, Byrne announced on his Twitter page that he and his wife Georgina were expecting their third child, and on Irish television it was announced that the baby was due around Halloween. Daughter Gia was born on 23 October 2013.
Godparents for the children are Byrne's sister Gillian Byrne and her husband Mark Gallagher and Georgina's sister Cecelia Ahern and Byrne's brother Adam McGarry Byrne. Byrne's father, Nikki Byrne Sr., died on 3 November 2009, from a heart attack. Westlife's promotional tour of the UK was cancelled as Byrne flew to Dublin to be with his family. Byrne Sr. sang part-time on Dublin's cabaret and karaoke scene and was presented with a Harley-Davidson motorbike by his son on his sixtieth birthday party the year before his death.