[a] Born and raised in Hohenems, Klien competed in Formula One for Jaguar, Red Bull and HRT, scoring 14 championship points across 51 Grands Prix.

On 2 February 2008 Klien signed as BMW Sauber's reserve and test driver for the 2008 Formula One season, alongside Estonian Marko Asmer.

[3] From 1996 to 1998, Klien won several kart races in both Switzerland and his native Austria, becoming the Suisse champion in his first year.

From there, Klien moved into the Formula Three Euroseries, with Mücke Motorsport, winning four races and finishing runner-up to Ryan Briscoe.

He finished alongside Cristiano da Matta and Nick Heidfeld in joint 16th in the Drivers' Championship.

After a promising performance in China, it was confirmed in December 2005 that Klien would drive for the Red Bull Racing outfit alongside David Coulthard for the 2006 season.

However, in Malaysia he collided with Kimi Räikkönen on the first lap and had to pit with suspension damage, before eventually dropping out with a hydraulic failure.

[10] After the two points finishes in Bahrain and Germany, there was some uncertainty as to where Klien would go next in his racing career, speculation suggested the United States as a logical choice for Klien, but he refused a ChampCar seat in a Red Bull-backed team for 2007, preferring to chase a Formula One drive with another team.

[11] As a result, the team announced that Klien had been fired for the last three races of the season in favour of test driver Robert Doornbos.

[12] On 15 November 2006, Honda Racing announced the signing of Klien as their test and reserve driver for the 2007 season.

[13] The Austrian made his debut for the Japanese works team at the Circuit de Catalunya, during the early pre-season testing during late November 2006.

At the 2007 British Grand Prix, he replaced the injured Jenson Button for the second free practice session on Friday.

[16] He also returned to Le Mans with Peugeot, finishing sixth overall in a 908 shared with Pedro Lamy and Minassian.

[1] Klien has taken part in a number of V8 Supercar drives, including the Bathurst 1000 where he teamed up with Russell Ingall.

[22] In 2017, Klien joined the Bundesheer (Austrian Armed Forces) and will continue his racing career in addition to military service.

[24] Klien competed in the 2021 Deutsche Tourenwagen Masters part-time by driving a McLaren for the Polish JP Motorsport team in a total of three two-race rounds.