Justin Welby has been speaking ahead of marrying the couple at St George's Chapel in Windsor.
The archbishop, who has attended a number of rehearsals for the ceremony, said of Prince Harry and Ms Markle as a couple: "They're a very, very sensible, they're a very self-possessed couple.
"And at the rehearsal they just got on with it and it was very relaxed, laughing and enjoyable."
Archbishop Justin also praised Prince Charles in stepping into the responsibility of walking Ms Markle down the aisle after her father was unable to attend the service.
He said Charles is "someone of great care and affection" adding, "he's a very warm person and that he's doing this is a sign of his love and concern and support. And I think it's wonderful. It's beautiful."
Speaking of Thomas Markle and the likelihood his illness will be mentioned during the prayers at the church, Welby said: "I really couldn't comment on that side of thing, except obviously as with all times like this where someone's ill you remember them in your prayers.
"And I hope people will pray for him, and pray for the couple and pray for everyone involved in the process tomorrow."
While Justin Welby will marry the couple, the service will be led by the Dean of Windsor Rt Rev David Conner and Most Rev Michael Curry (main image,right), the leader of the US Episcopal Church will preach.
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.