only started his cycling career at the age of 19, having been a runner before that. He became a professional road bicycle racer in 1999 for team Team Chicky World. After the team closed down, Sørensen switched to another Denmark based team, Team Fakta where he made a good name for himself on the Danish stage as one of the strongest cards of Team Fakta, securing himself a place on the Danish team for the 2000 Olympics. Before the 2001 season, Sørensen was on the verge of joining British Linda McCartney Racing Team but instead opted to stay in Denmark with Team CSC – World Online, as Team Saxo Bank was then known. In his first year with the team he participated in the 2001 Tour de France where he got a taste of success with a fourth place on stage 16. After then, Sørensen was a consistent part of the Tour setup for Team CSC, riding the biggest race in the cycling calendar every year from 2001 to 2005, his highlights including the overall GC rank of 20th in 2002. Another highlight was Sørensen's instrumental role in team captain Tyler Hamilton's win on stage 16 of the 2003 Tour de France when Sørensen, who was in a break away, sacrificed his own chances in order to pull Hamilton and thereby allow Tyler Hamilton to conserve the strength needed to win on the day. Nicki Sørensen started the 2005 season on a high note with a win in GP d'Ouverture la Marseillaise and a fourth place in Tour Méditerranéen during February, and during the season he prolonged his contract with Team CSC until 2007. In September Nicki Sørensen clinched stage 18 of the Vuelta a España after defeating Pascual Rodriguez in the sprint. On 16 July 2009, Sørensen won Stage 12 of the 2009 Tour de France. He was in an early breakaway with five other riders and attacked the small group with 20 km to cover to win solo. Sørensen retired after riding the 2014 Giro di Lombardia. The last victory of his career was the 2012 Gran Premio Bruno Beghelli.
Team management
After his retirement he remained with as a directeur sportif and coach. For the 2016 season he moved across to the Israeli Cycling Academy Team. In October 2016 the new team announced that Sørensen would join them as a sports director for their inaugural season in 2017. Aqua Blue Sport folded at the end of 2018.
Doping
In June 2015 prior to Anti Doping Denmark report he admitted to drug use in early part of his career.
