Speaking on BBC Radio 4's Today programme, the Archbishop of Canterbury said: "I am very, very sure after conversations that this is no tick-box exercise, 'we ought to get married in a church'."
Harry and Ms Markle announced their engagement on November 27 after dating for just over 18 months.
They are due to marry at St George's Chapel, Windsor Castle, in May.
"There is a profound sense of commitment, of seriousness, both about faith and their lives together, which is quite inspirational.
"It's important because people look at it and see a model of how two people commit their lives to one another before God in the presence of millions of people.
"It's always a beautiful moment - every wedding is profoundly beautiful. Even when you drop the rings it's still a very moving wedding."
He refused to confirm whether he would be conducting the ceremony, saying "I think that's up to them", but revealed he was looking forward to the big event, saying it would be "fun".
