Mrs Palin with Republican candidate Seneator John McCain
Elected Alaska's youngest and first woman governor in 2006
Grew up in Wasilla, near Anchorage, and was voted Miss Wasilla in 1984
Studied journalism and political science at University of Idaho
Is mother of five, including a son with Down's syndrome
Her husband Todd is an oil production operator
Likes hunting and fishing
But because it was kept a secret almost until the end, John McCain's choice did generate a fair amount of rumour and speculation.
Was he going to pick a traditional candidate, a safe bet - someone like the young governor of Minnesota, Tim Pawlenty, or would the veteran Arizona senator go for the wild card?
The answer came on a private jet that flew in from the Alaskan city of Anchorage on Thursday night and landed outside Dayton, Ohio, apparently carrying on board a woman, two men and two teenagers.
All the journalists who were covering the story started looking up the biography of Sarah Palin, the 44-year-old governor of Alaska.
'Average hockey mom'
She may be seen by some as a rising star of the Republican Party, but she was relatively unknown on a national level.
As he took to the stage, in front of a packed audience, Mr McCain introduced her as "exactly who I need, exactly who this country needs to help me fight the same old Washington politics of me first and the country second".
For observers, it showed Mr McCain felt he needed to make a bold move to help change the course of the race to the White House.
The two presidential hopefuls have been running head to head, with Mr Obama gaining eight percentage points in the polls in recent days.
The choice of Sarah Palin is a high risk bet that could bring high rewards, but there are no guarantees.
Mrs Palin, a mother of five, is the first woman to be on a Republican presidential ticket.
Married for 20 years to Todd Palin, her high school sweetheart, she was nicknamed "Sarah Barracuda" during her college years for her aggressive basketball playing style - the name has stuck.
On stage, dressed in a conservative black power suit, her hair raised in a high ponytail, she described herself as "an average hockey mom from Alaska".
She drew applause when talking about her anti-corruption drive, her standing up to big oil companies and even the "good old boys club", which drew a smile from Mr McCain.
She eats moose meat and is an inveterate hunter, a lifelong member of the National Rifle Association (NRA).
One of her sons is heading to Iraq in September. The other, born in April, is diagnosed with Down's syndrome.
In many ways, her story is all American and her values will appeal to the conservative base and to blue-collar voters.
With 80% approval ratings back home, she seemed to also get the approval of the crowd she was addressing, drawing very enthusiastic cheers, as she spoke in a relaxed, accessible way.
Mrs Palin also ticks several required boxes - she is fiscally conservative, in favour of drilling for oil and very staunchly anti-abortion.
Most of all she is a reformer and a fresh face for the Republican ticket.
President George W Bush said she was "an exciting choice" and Mrs Palin certainly adds energy and sizzle to the McCain campaign.
She also clearly reached out to disaffected Hillary Clinton supporters, who are disappointed their candidate did not make it on to the Democratic ticket, not even as vice-president.
"I can't begin this great effort without honouring the achievement of Geraldine Ferraro in 1984 and of course, Hillary Clinton, who showed determination in her presidential campaign," Mrs Palin said.
"It was rightly noted in Denver this week that Hillary left 18 million cracks in the highest, hardest glass ceiling in America. But it turns out the women of America aren't finished yet, and we can shatter that glass ceiling once and for all."
The Democrats for McCain group sent out an e-mail saying its supporters, especially the women, were "ecstatic" about the choice of Mrs Palin.
But other Democrats said they felt insulted that Mr McCain thought he could woo women by just putting any woman on his ticket, with one sentence making the rounds: "Palin, you are no Hillary Clinton".
It all made for an exciting day in Dayton, a city of just over 150,000 that has been hard hit by job losses in the past few years.
But the whole of the US is probably now scouring the internet for more information about Governor Palin and trying to assess her credentials. Many will be wondering whether she is ready to be vice-president and even lead the US, should something happen to Mr McCain if he is elected president.
As commander of the Alaska National Guard, she visited troops in Kuwait last year, but has a very thin foreign policy background.
Similarly, while she does have executive experience, the Obama campaign wryly pointed out she had been the mayor of a town with just 9,000 people.
As governor of Alaska during the past two years she has gained more experience, but even some Alaskans calling into talk shows on US network television said they doubted whether that had prepared her for the challenge of national politics.
She did herself no favours in a recent interview.
"As for that VP talk all the time, I can't answer until someone answers me. What is it exactly that a VP does every day?" she said just a month ago on CNBC when asked about her chances of being on the ticket.
"I'm used to being very productive and working real hard in an administration. We want to make sure that this VP slot would be fruitful type of position especially for Alaskans and for the kind of things we are trying to accomplish here for the rest of the US."
By choosing her, Mr McCain may have undercut his best attack against Senator Obama - if he uses the inexperience card now it will be turned against him and his running mate.
While conservatives, such as radio host Rush Limbaugh and former Bush adviser Karl Rove, hailed the Palin surprise, there were also dismayed reactions from some Republicans, who felt the choice underscored Mr McCain's weaknesses and was too risky.
Polls in the coming days, and Mrs Palin's performance at the Republican National Convention, will help assess the impact of Mr McCain's decision.
In the meantime, Mr McCain and his new partner have something else to worry about - Mrs Palin is facing an investigation in Alaska for alleged abuse of power involving her former brother-in-law. Her deposition is expected to be scheduled soon.
She says she has "nothing to hide" and is "cool" about the investigation.