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.
"Ronan has been working in Australia a lot on 'The X Factor' and he loves it. He's already been spending half of the year there and is planning to make the move permanent. Obviously he will make plenty of trips to Ireland to see his family and children.
"He genuinely loves Yvonne and always has, and regrets the situation, but is doing his level best to cope with it and keep things steady for their kids."
A second source added to the Daily Mirror newspaper: "Once the Aussie 'X Factor' auditions begin in May don't expect him back. He did hope to patch things up again with Yvonne, but all the time in the world couldn't mend all the problems they have going on behind the scenes."
Yvonne said in a statement last night: "Sadly, our marriage ended late last year. We kept this news private to give everybody involved time to adjust."