Republican presidential hopeful John McCain named the youngest and first female governor of Alaska, Sarah Palin, as his running mate today.
"Governor Palin is a tough executive who has demonstrated during her time in office that she is ready to be president," Mr McCain said in a statement announcing the choice.
In an election which will be about change, so-called “hockey mum” Ms Palin is virtually unknown outside Alaska, where she has a reputation for government reform and an approval rating higher than 80 per cent.
The 44-year-old former runner-up of the 1984 Miss Alaska beauty pageant will be the second female vice-presidential nominee of a major party, following Geraldine Ferraro as Democratic nominee in 1984.
Democratic nominee Barack Obama is making an aggressive play for the traditional Republican stronghold of Alaska and its three electoral votes, and polls show the race is close.
Whoever wins, America will either have its first black president or its first female vice president in history.
At a raucous rally in the swing state of Ohio, Mr McCain said he made his pick after looking for a political partner “who can best help me shake up Washington and make it start working again for the people who are counting on us”.
He said Ms Palin was “exactly who I need” and “exactly who this country needs to help us fight the same old Washington politics of me first and country second”.
To huge cheers, Ms Palin said she wanted to honour the former first lady who had shown “such determination and grace in her presidential campaign”.
“But it turns out the women of America aren’t finished yet and we can shatter that glass ceiling once and for all,” she said.
“If you want change in Washington, if you hope for a better America, then we’re asking for your votes on the fourth of November.”
The choice of Ms Palin is apparently aimed at appealing to women voters who might have been disillusioned by Mr Obama's decision to pick Mr Biden instead of Democratic Senator Hillary Clinton.
Ms Palin is a conservative first-term governor of Alaska with a strong anti-abortion views and a record of fiscal conservatism. She is also a member of the National Rifle Association.
She has irked environmentalists by opposing the listing of the polar bear as a threatened species and is a big supporter of oil and gas drilling off the Alaska coast.
Ms Palin, former mayor of the town of Wasilla, built a reputation as a reformer in a state that recently has been hit with corruption scandals. Elected in 2006, she is Alaska's first woman governor.
Ms Palin and her husband, Todd, have five children, ranging in age from 18 years to 4 months.
She is an avid sportswoman who Republicans hope would bring youth and vitality to the ticket. Mr McCain is 72.
Ms Palin is not well-known nationally, and that could cut into Mr McCain's argument that Mr Obama is too inexperienced to handle the White House.
If elected, she would be the first woman US vice president.
In his acceptance speech last night, Mr Obama directly attacked Mr McCain and linked him to what he called the failed Republican economic policies of President George W. Bush.
The Republican National Convention is scheduled to begin on Monday in St Paul, Minnesota.
However, it has been reported that party officials are considering delaying the start of the convention as Tropical Storm Gustav threatens the Gulf Coast.