Born in Grimstad, Aust-Agder, Norway, Thor won the under-23 time trial world championship and the under-23 versions of Paris–Roubaix and Paris–Tours before turning professional in 1998. He was Norwegian time trial champion in 2004 and 2005 and road race champion in 2004 and 2010. In 2006, he won seven UCI ProTour races and two stages of the Tour de France. He won the prologue in Strasbourg and led after the first day despite a cut arm. He continued with stitches and regained the yellow jersey after stage 2 with a third place. He won the last stage, beating Robbie McEwen in a sprint, thus making him the only person to win the first stage or prologue and the last stage of the Tour de France in the same year. In the 2006 Vuelta a España he won stage 6, wore the golden jersey for three stages and won the points classification At the 2008 Tour de France, Hushovd won stage 2 in a bunch finish.
2009
In 2009, Hushovd rode for the. He took one of the team's first victories of the season by winning Stage 3 of the Tour of California. At the Tour de France, he won green jersey for the points classification for the second time, ahead of Mark Cavendish. Typically the sprinter with the most stage victories wins the points classification, though Thor only won one stage, stage 6, while Cavendish won six. After a controversy on stage 14, where Cavendish was relegated to the back of the peloton for impeding Hushovd, Hushovd attacked alone on stage 17, a mountain stage, winning two intermediate sprints. Hushovd won stage 3 at the Tour of Missouri – over rolling hills – in September 2009, in a sprint finish.
2010
On 9 May 2010, Hushovd broke his collarbone on a training ride after colliding with a young girl. At the Tour de France, Hushovd won the third stage, which was an unusual one for the Tour since it featured of cobblestones. He prevailed in the sprint involving five other riders. That victory netted him the Green jersey, but he ultimately lost it to Alessandro Petacchi of the team. On 3 October 2010, Thor won the road world championship, which started in Melbourne and finished in Geelong, Australia. He was the first Norwegian to win the rainbow jersey. VeloNews said: "Hushovd...dominated a bunch sprint at the end of a thrilling 267km race, beating Denmark's Matti Breschel and Australia’s Allan Davis." The favorite, Philippe Gilbert, was caught with three kilometers to go.
In 2012, Hushovd joined on a three-year contract. Suffering from a then unknown medical condition, he had to abandon the Giro d'Italia and cancelled his scheduled participation to the Tour de France and Olympic road race. The medical impairment was later identified as a "virus and muscle inflammation" by team doctors. Thor hardly achieved any notable result in the season except fourteenth at Paris-Roubaix. In October, he said that he hoped to put the bad year and the virus that ruined it behind him and that he was optimistic and motivated about the 2013 season.
Thor currently resides in Monte Carlo, Monaco, with his wife Susanne, and their daughter Isabel. The Hushovds also maintain an offseason residency in Grimstad, Aust-Agder, Norway.