Buemi had taken part in winter testing for Toro Rosso
Sebastien Buemi will drive for Formula One's Toro Rosso team this season.
The 20-year-old Swiss, who was widely tipped for the job, is likely to be the youngest driver on the 2009 grid.
Dietrich Mateschitz, boss of Toro Rosso and sister team Red Bull Racing, had earlier said Buemi was "very likely" to be chosen having impressed in testing.
"I will do all I can to bring home the best possible results and to show Red Bull that the confidence it has shown in me is justified," said Buemi.
Last year Buemi competed in the GP2 support series and spent time as reserve driver for Red Bull Racing. His team-mate at Toro Rosso has yet to be named.
Buemi fills the gap left by Sebastian Vettel's promotion from Toro Rosso to Red Bull, after his impressive 2008 campaign, which saw him become the youngest Grand Prix winner in history at Monza.
I want to thank Red Bull for this opportunity and for all the help they have given me in my career
Vettel in turn takes up the vacancy left by the retirement of David Coulthard.
"I am naturally very happy to be driving for Toro Rosso this year," said Buemi.
"Being an F1 driver has always been my target, since I first started racing.
"I want to thank Red Bull for this opportunity and for all the help they have given me in my career, dating back to 2005."
Former team co-owner Gerhard Berger had strongly hinted that Buemi would win a drive when he said in a magazine interview that the 20-year-old would be a "good and fast driver" for Toro Rosso.
Team principal Franz Tost praised Buemi's speed and "ability to learn and progress" during testing.
"That, along with some impressive performances in GP2 was enough to convince us to give him the drive," he added.
Buemi's first official outing as a Toro Rosso driver will be in testing at the Portimao Circuit in Portugal later in January.