Wearing a frilly cream lace gown, the third in line to the throne was carried into the Chapel Royal of St James's palace by his father, his mother Kate close by, elegant in a cream Alexander McQueen outfit.
Queen Elizabeth II and the couple's parents and siblings, including William's younger brother Prince Harry, were among just 22 guests at the ceremony, including seven newly-named godparents.
Archbishop of Canterbury Justin Welby, the spiritual head of the world's Anglicans, performed the baptism, which involves pouring holy water from the River Jordan on the baby's head.
Television pictures showed the light-haired George Alexander Louis appearing wide awake and calm. He even gave the semblance of waving at the 87-year-old queen, his great-grandmother, when his father moved his arm up and down.
Prince William holds his son as he arrives at Chapel Royal in St James's Palace for the christening of the three month-old baby.(AFP photo)
"He's all ready," William, 31, told the assembled party, which included his father Prince Charles and his wife Camilla, adding: "So far so good."
The relatively low-key ceremony reflects the fact that the Duke and Duchess of Cambridge want their son to have a relatively normal upbringing and have closely guarded his privacy. He has only appeared in public once before, when they left hospital after his birth on July 22.
The couple broke with tradition by naming only one royal, William's cousin and champion horse-rider Zara Philips, among the godparents, with the others being childhood, university and work friends.
The ceremony welcomes Prince George into the Church of England, which he is destined to lead as future king and "Defender of the Faith".
Harry and Kate's sister Pippa Middleton, who had both been wrongly tipped as potential godparents, both read passages from the Bible.
Prince William and his wife Kate with Prince George during his christening by the Archbishop of Canterbury at Chapel Royal in St James's Palace in London. (AFP photo)
Each of the godparents was asked to commit to providing Prince George with guidance as he grew up.
They include Zara Phillips, pregnant with her first child with rugby player husband Mike Tindall; William's childhood friends William van Cutsem and Earl Hugh Grosvenor; Julia Samuel, who was close to William's mother Diana; and Emilia Jardine-Paterson, who went to the private Marlborough College with Kate.
Rounding out the list are Oliver Baker, a friend from St Andrew's University in Scotland, where the royal couple met, and William's long-time aide Jamie Lowther-Pinkerton, a former soldier in the elite SAS army unit.
A very special moment
A handful of royal fans camped overnight outside the palace hoping for a glimpse of the queen and her three direct heirs -- Prince Charles, his son Prince William and baby George, who is third in line to the throne.
Royal supporter Terry Hutt waits opposite St James's Palace in London, as Prince George of Cambridge is baptised inside Chapel Royal.(AFP photo)
"This is a very special moment. We will see three kings in the making," said John Loughrey, a 58-year-old fan wearing a raincoat bearing the pattern of the Union Jack flag.
He slept out overnight in the rain, but told AFP it did not bother him, adding: "This is a unique, historic moment."
The Duchess of Cambridge carries Prince George after his christening. (Reuters photo)
In the House of Commons, Prime Minister David Cameron urged lawmakers to "join me in celebrating" the event.
The christening was sharp contrast to the Duke and Duchess of Cambridge's lavish 2011 wedding, which was broadcast live on televisions across the world, and to the media frenzy surrounding the birth of their first child.
Just six members of the royal family attended, along with Kate's parents Michael and Carole Middleton and her siblings James and Pippa.
The service was conducted behind closed doors although an official photograph by celebrity snapper Jason Bell will be released to the public on Thursday.
Afterwards the guests were invited for tea at Charles's official London residence, Clarence House, where a portion of William and Kate's wedding cake was to be served.
It is traditional for Christian couples in Britain to save a tier of the cake -- normally fruitcake encased in icing -- for their first child's christening.
The official photos are expected to gain iconic status, the first time four generations of monarchs have been pictured together since 1894, at the christening of the future king Edward VIII.
Patrick Jephson, Diana's former private secretary, said the christening sent a strong message about the royal family's durability as a dynasty.
"It reinforces the public perception that the British royal family is going to be around for a long time to come," he told AFP.
Queen Elizabeth II speaks with Prince William and Kate as they arrive with their son Prince George at the Chapel Royal in St James's Palace.(AP photo)