George, who was born July 22, wore a replica of an intricate lace-and-satin christening gown made for Queen Victoria's eldest daughter and first used in 1841.
When William was christened in 1982, he wore the original gown — by then well over a century old — but that gown has become so fragile that a replica was made.
The infant, who will head the Church of England when he becomes king, was christened with water from the River Jordan by Archbishop of Canterbury Justin Welby.
He arrived at the chapel in his father's arms with his mother by their side.
Kate, smiling broadly on her way into the chapel, wore a cream-colored Alexander McQueen dress and hat by milliner Jane Taylor with her long hair brushed to the side. William wore his customary dark suit and tie as he proudly carried their child.