The wedding took place on 29 July 1981. 3,500 guests made up the congregation at St Paul's Cathedral. Charles and Diana selected St Paul's over Westminster Abbey, the traditional site of royal weddings, because St Paul's offered more seating[ and permitted a longer procession through London.

The ceremony was a traditional Church of England wedding service, presided over by the Most Reverend Robert Runcie, Archbishop of Canterbury, and the Very Reverend Alan Webster, Dean of St Paul's Cathedral. Two million spectators lined the route of Diana's procession from Clarence House, with 4,000 police and 2,200 military officers to manage the crowds. The security increased and sharpshooters were stationed due to the potential threat of an attack by the Irish Republican guerrillas. The security screenings in the airports also increased. The cost of the wedding was later estimated to be $48 million in total (between $70M and $110M when adjusted for inflation), with $600,000 being spent on security. Regiments from the Commonwealth realms participated in the procession, including the Royal Regiment of Canada.

At 10:22 BST the Queen and the royal family were taken to the cathedral in eight carriages, the Prince of Wales in the 1902 State Landau, which was later used following the ceremony to take the couple back to Buckingham Palace. Lady Diana arrived at the cathedral in the Glass Coach with her father, John Spencer; she was escorted by six mounted Metropolitan Police officers. She arrived almost on time for the 11:20 BST ceremony. The carriage was too small to hold the two of them comfortably due to her voluminous dress and train. As the orchestra played Trumpet voluntary, an anthem by Jeremiah Clarke, the bride made the three-and-a-half minute walk up the aisle.

Diana accidentally changed the order of Charles's names during her vows, saying "Philip Charles Arthur George" instead of the correct "Charles Philip Arthur George". She did not promise to "obey" him as part of the traditional vows. That word was eliminated at the couple's request, which caused a sensation at the time. Charles also made an error. He said he would offer her "thy goods" instead of "my worldly goods". In keeping with tradition, the couple's wedding rings were crafted from Welsh gold from the Clogau St David's mine in Bontddu. The tradition of using Welsh gold within the wedding rings of the Royal Family dates back to 1923. Upon marriage Diana automatically acquired the title of Princess of Wales.