The former England footballer wore his OBE medal pinned to his Ralph Lauren morning suit. Medals are traditionally worn on a man's left breast, above the heart, but Beckham chose to wear his on the right.
Victoria wore a midnight blue dress which she designed herself, taken from her autumn/winter 2011 collection.
She accessorised with an elegant Philip Treacy pillbox hat perched on the front of her head, and a pair of Christian Louboutin stilettos customised in collaboration with Louboutin himself.
The Beckhams were invited to the royal wedding because David became close to Prince William when they worked on England's World Cup bid.
The LA Galaxy player said earlier this week: "I think a royal wedding really is amazing. Our country needs it. Our country wants it. The British public love the Royal family.
"I was brought up loving the Royal family. I took my nan and granddad to Buckingham Palace when I got my OBE. They were so proud. It means so much to them."
Etiquette watchers pointed out that the footballer had committed a faux pas by wearing his OBE on the wrong side.
Chelsy Davy, girlfriend of Prince Harry, preceded the Beckhams into the Abbey.
The 25-year-old has chosen not one, but two outfits for the day, both tailor-made by Alberta Ferretti.
For the Abbey, she wore an aqua green satin dress with matching boat-neck jacket. She will change for the Buckingham Palace evening reception into a glamorous one-shoulder crepe satin gown in midnight blue, with a cut-out detail on the back.
Other famous guests included Tara Palmer-Tomkinson in a striking, bright blue Philip Treacy hat.