Having represented Australia in the Junior Team in 2013 and the U21 team in 2014, in 2015 Purnell raced in the Men's U23 Quad Scull in Plovdiv, Bulgaria. Purnell went on in 2015 to win bronze in the event, while in 2016 he raced in the Men's Eight at the U23 World Championships. In 2017, Purnell was been named in the Men's Eight for World Cups 2 and 3 and the World Championships. In 2018, Purnell was named as a reserve for the Men's Australian Rowing Team, covering both sweep and sculling boats, however post World Rowing Cups, he won selection to the Men's Quadruple Scull for the 2018 World Rowing Championships. The younger brother of Australian rowing Olympian, Nicholas, the younger Purnell is also a member of the Reinhold Batschi Men's National Training Centre and likes to listen to Two Strong Hearts by John Farnham before going out on the water.