George, who is third in line to the British throne, was born on July 22.
The royal family said the christening would be a private affair, but photographs will be taken after the service.
The names of godparents will be released nearer the time, a royal spokeswoman said, although it is rumoured that William's brother Prince Harry and Catherine's sister Pippa will be among them.
The announcement came after William and Catherine's new coat of arms was released.
Approved by Queen Elizabeth II, it combines William's coat of arms and his wife's shield from the Middleton family coat of arms.