Kate, 30, has been struggling with severe morning sickness but is well enough to accept the invitation to the BBC's Sports Personality of the Year Awards in London, her office says.
She will be presenting two top awards, including the main sports personality of the year award.
Her first official appearance since her pregnancy announcement follows a year of top level sports action in the U.K., peaking with the Summer Olympics in London. She and husband William along with Prince Harry were ambassadors to the British Olympic and Paralympic teams and watched several events.
In a statement issued just hours before she heads to one of the London Olympics venues in South London, a St. James's Palace spokesman tells PEOPLE: "The Duchess of Cambridge will tonight attend the BBC's Sports Personality of the Year Awards at the ExCeL London, where Her Royal Highness will present the Lifetime Achievement and the main Sports Personality of the Year Awards. The Duchess will attend the event in response to a longstanding invitation from the BBC."