[6] Three days after turning professional Colsaerts entered 2000 Qualifying School where he gained his European Tour card.

[10] Colsaerts led the Nissan Irish Open at the halfway stage in 2006,[12] but fell away over the weekend and finished in a tie for 53rd place.

[10][15] Colsaerts nearly won the 2009 Challenge of Ireland after a final round 68, but lost at the third hole of a sudden-death playoff to English golfer Robert Coles.

[26] Prior to all of this, he had only just advanced from the group stage after defeating Charl Schwartzel at the first playoff hole.

[29] Colsaerts played in the 2012 U.S. Open at the Olympic Club and made the cut for the first time in a major championship, going on to finish tied 27th.

On 27 August 2012, he was selected by European captain José María Olazábal as a wildcard for the 2012 Ryder Cup team, becoming the first Belgian to play in the event.

[32] In October, Colsaerts joined the PGA Tour, accepting Special Temporary Member status for the final three events of the season.

[33] Colsaerts made $677,011 as a non-member, finishing almost $30,000 ahead of Kevin Chappell, the golfer who earned the 125th and final PGA Tour card for 2013.

In August 2016, Colsaerts represented Belgium at the 2016 Summer Olympics in the Individual Stroke Play competition, finishing tied for the 30th place.