The pair will recite the strongest act of penitence from the 1662 Book of Common Prayer at the service, conducted by Archbishop of Canterbury Rowan Williams.
The prince will also pledge to be faithful to his new wife.
The prayer, released Thursday by Clarence House, the prince's household, is worded: "We acknowledge and bewail our manifold sins and wickedness, which we, from time to time, most grievously have committed, by thought, word and deed, against thy Divine Majesty, provoking most justly thy wrath and indignation against us.
"We do earnestly repent, and are heartily sorry for these our misdoings."
800 guests including celebrities, politicians and royals are to attend the ceremony in St George's Chapel, Windsor Castle, and a champagne buffet reception.
Earlier, 28 close family members will attend the civil ceremony in Windsor Guildhall.
The queen and Prince Philip will not attend that ceremony but will host a lunch for visiting foreign royals.