Cameron said he had found the Prince to be "a remarkable young man" after spending time with him in Zurich for England's recent failed bid to host the World Cup.
The PM said he was confident it would be "a great moment for Britain", adding that William and fiancee Kate Middleton were "a wonderful couple".
"I know it will be a huge success, not just for the country and I think the world looking at Britain and how we have this wonderful Royal Family and Prince William, who I've spent some time with recently, is a remarkable young man - great, balanced, poised," the Sky News quote Cameron as saying about the royal wedding.
"I think he will make I am sure a fantastic husband and one day he will make a wonderful king.
"I think the world will be looking at this royal wedding but I think we will be very proud of it in the UK, but above all it's two young people who love each other very much.
"They are getting married and we should be very happy for them," he said.
Speaking to CNN, Cameron said he had "spent some time" with the Prince - a fellow Old Etonian - in Zurich in December.
"It was great to hear, you know, when someone's getting married, the excitement, the enthusiasm. I could very much feel it," he said.
Whether it would be a budget wedding given the Government's austerity measures?
"No, it will be a royal wedding that the whole country can celebrate," the PM replied. (ANI)