When he became leader of the National Party in opposition in 2006, replacing Don Brash, Key had only been in parliament for four years.
Doubters wondered whether he knew how to play the game when the going got tough.
He did.
When two years later he won the New Zealand national election, he broke the mould of long-serving career politicians like Helen Clark and Jim Bolger who preceded him.
He was laid-back, easy to talk to, unpretentious and highly approachable, which made him a hit with voters from the start.
He was young, fresh, different and the most media-friendly prime minister in decades.
Former ACT leader Richard Prebble described him as "coming straight out of central casting".
There was steel in Key, forged during his climb to the top of international investment banking and currency trading.
The 55-year-old wasn't born rich.
Key and his two sisters were raised in a Christchurch state house by his Austrian-Jewish immigrant mother after his father died, leaving the family in debt.
He talked often of his mother, holding her up as an example of someone who worked hard to care for her family in the face of adversity.
Key went to local schools and met his wife Bronagh at Burnside High.
From Burnside he went to Canterbury University, graduating with a bachelor of commerce degree in 1981.
Key studied business management at Harvard before finding his first job as project manager of a Christchurch-based clothing manufacturer.
After two years he headed for Wellington and a job at Elders Merchant Finance as a foreign exchange dealer, earning quick promotion to head trader.
Key was head-hunted by Bankers Trust in Auckland, where he stayed for seven years before Merrill Lynch discovered him and in 1955 made him head of Asian foreign exchange in Singapore.
Key's career had taken off, and in the same year Merrill Lynch appointed him head of foreign exchange in London.
It's been reported he was earning about $NZ5 million a year, and making his personal fortune on the exchange market at the same time.
Key returned to New Zealand as a rich man seeking new challenges, and settled into an $NZ8 million mansion in Auckland.
He intended being prime minister from the day he entered parliament, determined to lift New Zealand's economic achievement and make it a better country to live in.
Today, he again showed he is a man who makes his own decisions - announcing he would quit as prime minister on his own terms, for his own reasons.
"I just feel it has been a decade of a lot of nights home alone for (Bronagh). It is the right time for me to come home."
