Tony Blair says his wife Cherie made him a Catholic.
Speaking in Italy on Sunday, the former British Prime Minister said: "Frankly this all began with my wife.
"I began to go to Mass and we went together. We could have gone to the Anglican or Catholic church - guess who won?"
Blair was speaking for the first time about his 2007 conversion.
Blair, who was addressing an audience of some 15,000 at an annual religious conference in Rimini in Italy, said that switching to Catholicism was like "coming home" and is now "where my heart is."
"As time went on, I had been going to Mass for a long time... it's difficult to find the right words. I felt this was right for me. There was something, not just about the doctrine of the Church, but of the universal nature of the Catholic Church."
Blair, who spoke in Italian, said: 'It is a pleasure always to be in Italy. It is here in this country that I have spent many happy times and where 30 years ago, almost to the day, I proposed to my wife and three decades and four children later, I at least am still pleased to recall the memory.
"Ever since I began preparations to become a Catholic I felt I was coming home and this is now where my heart is, where I know I belong."
Blair closed his address by saying: "It would be a great sign of reconciliation and hope if the Holy Land were a place for reconciliation and peace."
Three million people in the world are descended from one Irish High King