 In 2010, he attended the University of Illinois for which he won the individual 2011 Jack Nicklaus Invitational and the individual 2012 NCAA Division I Championship in his second year; the next year, he finished second with his team at the 2013 NCAA Division I Championship and won the individual 2013 Big Ten Conference Championship.In summer 2013, Pieters decided to forgo his senior year at the University of Illinois and turn professional.He made his debut on the European Tour in July at the Alstom Open de France, where he finished 29th; at the end of the year, he battled through all three stages of the European Tour Qualifying School taking the 20th card at the Final Stage, and qualified to play on the European Tour.