The royal couple was among the audience at the event at London's Royal Albert Hall, which featured singers Gary Barlow and Will Young.
The Duchess, formerly known as Kate Middleton, dazzled photographers in a teal Jenny Packham gown, while William wore a dinner suit.
The prince said on Friday he could not wait for the Games to begin, and encouraged Britain's Olympics and Paralympics athletes in a speech, saying: "Glory awaits you."
The Olympics will take place July 27-August 12.
