The UK grew 0.8% in the three months to September, according to figures released by the Office of National Statistics.
Following strong growth in the second quarter, this represents the strongest 6-month growth figure for over 10 years.
On the same day as the GDP figures beat analysts' expectations, credit rating agency Standard & Poor's revised the UK's AAA rating from negative to stable.
Praising the government's actions to put Britain's public finances "on a more sustainable footing", the agency said that "the coalition government's policy objective to close the fiscal gap further underpins the ratings."
Welcoming both pieces of news, Chancellor George Osborne said:
"This is a double dose of good news for the British economy. In an uncertain global economy this will help to underpin confidence in the recovery."