The 35-year-old Boyzone star had been trying to salvage his 14-year-union with wife Yvonne, 37, following his 2010 affair with backing dancer Francine Cornell.
However, the pair have admitted defeat and confirmed their split. He tweeted: "Sadly our news is true. Thank you all for your support.
"Yvonne and I still love and care for each other and want to protect our kids."
It is thought Ronan - who has children Jack, 13, Marie, 11, and six-year-old Ali with Yvonne - will now move to permanently Sydney, where he works as a judge on 'The X Factor'.
A source said: "Really things never recovered after Ronan's affair. They've been determined to do their best for the sake of their children, but things have finally reached a head.