Purchase began in 1999 with the rowing. In 2003 and 2004 he took part in the Junior World Championships. His breakthrough came in the 2005 season, when he was first in the World Cup at the event at Dorney Lake and Fourth on the regatta course in Oberschleißheim second. Finally, he was at the U23 World Championships in Amsterdam champion and won at the 2005 World Championships in Gifu the silver medal behind the Greeks Vasileios Polymeros. 2006 then became his most successful season so far. He first came to the Lucerne Rotsee to his first World Cup victory. Then in August 2006 he won at the World Championships on Dorney Lake the title in the lightweight single sculls.
Since the lightweight one is no Olympic boat class, moved Purchase in the pre-Olympic season in 2007 in the lightweight double sculls. Together with Mark Hunter, he reached the World Cup twice second and once third place at the World Championships took two third place. In the World Cup 2008 season was dominated by both the British and won all three events. Also at the 2008 Olympics achieved by the two a sure win.
After a year break, the two returned in 2010, according to a World Cup victory in Munich and a fifth place in Lucerne, the two won at the World Championships in New Zealand. Your title they could successfully defend in Bled a year later. At the Olympic Games in 2012, the two Englishmen were subject to the Danes Mads Rasmussen and Rasmus Quist.