The Donegal-born star made the announcement on his website on Friday and asked his fans to pray for his wife Majella.
"She is undergoing treatment at present and as it was found in the early stages we are very hopeful of a full recovery," he said.
"All we need are your prayers to help us through this difficult time and we know we can rely on that."
The couple has been married since 2002 after first meeting in Tenerife in 1999.
Majella, 53, has been heavily involved in her husband's music career and has often joined him on stage to perform a duet.
On his website Daniel said it felt like they had known each other their entire lives, describing Majella as 'down-to-earth, funny and very much her own person with an understated self-confidence'.
Majella has two children from a previous marriage, 25-year-old Michael and Siobhan who is 22.
Following the announcement many fans have taken to social networking sites to wish the pair well as Majella's treatment gets underway.