Farrar started racing at 13, and rode for Jelly Belly in 2003, Health Net-Maxxis in 2004, and Cofidis in 2006 and 2007. In April 2006 he crashed near the finish of the Circuit de la Sarthe and broke his collarbone and missed most of the season. For the 2008 season, he transferred to Slipstream-Chipotle.
He has won stages in the Giro d’Italia, Vuelta a España, Three Days of De Panne and Tour de France. He wore the yellow jersey on stage three of the 2008 Tour of California after winning intermediate sprint points during stage two.
Farrar is very popular in Flanders, because he is fluent in Dutch and lives in the Belgian city of Ghent.
In May 2011 Farrar, together with the entire Leopard Trek team, withdrew from the Giro d’Italia as a mark of respect for his friend and training partner Wouter Weylandt, who was killed in an accident during the race.
On July 4, 2011, Farrar won his first Tour de France stage, Stage 3 from Olonne-sur-Mer to Redon, becoming the first American to win a stage of the Tour on the Fourth of July.