The split is said to be "amicable" and the pair said they would continue to provide the best for their children.
A statement issued on the couple's behalf said: "With great sadness, Ronan and Yvonne Keating today announce their separation.
"The separation is amicable and they will continue to work together in order to provide the best for their children.
"The family ask for privacy at this difficult time."
A spokesman said there would be no further comment.
Keating and his Irish model wife have three children, Jack, Marie and Ali.
The pair had known each other since their early teens, but married within months of beginning a relationship.
Keating and the then Yvonne Connolly tied the knot on the island of Nevis in the Caribbean in April 1998, and their first child, Jack, was born within a year.
He has spoken in interviews about how meeting his wife prompted him to give up a whirl of partying and one-night stands which he had briefly enjoyed while touring with Boyzone.
Talking about the life-changing experience, Keating once said: "A lot of the time I was dating and there would be girls throwing themselves at me. I'd say, 'no, no, no. I can't'.
"And then there was the first time I had a one-night stand. I left my girlfriend the next day. I called her and said, 'I can't be with you any more'. I went through this brilliant stage of being with a different girl every other night. Then I met Yvonne and everything changed."
The pair's beach marriage came less than three months after the death of Keating's mother Marie from breast cancer.
He asked her to marry him on a whim after they had been for a walk and the ceremony was held shortly after.
They had a church blessing in Ireland a year later with friends and family.
Speaking of their relationship, in one interview, he has said: "I've said it before and I'll say it a thousand times, my wife is everything to me. She's my rock, the love of my life. I'm very lucky."
The death of Gately in October was a huge and unexpected blow to Keating and the rest of his bandmates.
They had been recording together again and had played a number of live shows after reforming to tour in 2008.
Keating - whose hits have included Life Is A Rollercoaster - joined the rest of the band as pallbearers at the funeral.