Donald turned professional in 2001 and has since developed a reputation as one of the most consistent golfers. His most successful season to date was arguably in 2004 when he won the Omega European Masters and the Scandinavian Masters by Carlsberg. The same year he also triumphed at the WGC World Cup with Paul Casey.

These victories earned him a wild card in Bernhard Langer抯 Ryder Cup team in 2004 at Oakland Hills where he won twice in Europe抯 record breaking victory. He made the team again in 2006, winning 3 out of 3 matches as Europe triumphed once more. Having undergone wrist surgery in 2008, he came storming back the following season with 4 top ten finishes including joint 5th place at the 138th Open Championship.

He continued in fine form in 2010, finishing joint 2nd at the BMW PGA Championship and winning the Madrid Masters by one shot for his first title in four years. Donald's biggest win to date came in February 2011 at the WGC-Accenture Match Play Championship when he defeated the world number one Martin Kaymer 3&2 in the final.

Donald抯 winning streak continued when he went on to beat Lee Westwood in a playoff to win the European Tour's flagship event the BMW PGA Championship. This was Donald's fifth victory on the European Tour and in the process achieving one of the games highest accolades of becoming the world number one. His first victory as world number one came at the 2011 Barclays Scottish Open. He won his fourth title of the year at the Children's Miracle Network Hospitals Classic in October 2011. With the win, he secured the PGA Tour money list title. In December, Donald secured the European Tour Race to Dubai for 2011, becoming the first golfer to officially claim top rank on both PGA Tour and European Tour money lists in the same year.

2012 saw Donald face competition for his spot atop of the rankings, losing it briefly to Rory McIlroy before only two weeks later winning the Transitions Championship in a four-man playoff to regain it. On 15 April 2012, Donald again lost the number one ranking to McIlroy, cutting cut short his second term as the world's number one player, ending after a four week spell. However, Donald finished 3rd at the Zurich Classic of New Orleans to reclaim the Number One rankings. This took Donald to 45 weeks at Number One which is sixth in the all time ranking.