Cassie Patten represented Great Britain at the Beijing 2008 Olympic Games in the 800m freestyle where she reached the final and in the 10km open water-swimming event, where she won a bronze medal.
Patten attended Plymouth College as a swimming scholar from the age of 11-18 and competed at her first international meet in 2003 at the European Short Course Championships Dublin, where she came 15th in the 200 Fly.
At the British Championships in 2006, she won a bronze in the 400m IM and silver in the 800m Freestyle. Then at the British Championships in 2007, she won a bronze in the 400m freestyle and silver in the 200m Fly. In 2008, her third year at the Championships she won silver in the 800m freestyle.
In 2007 Patten won silver in the 10km open water-swimming event at the World Championships in Melbourne, despite being stung by jellyfish. A year later she took silver once more, just three seconds behind Larisa Ilchenko (RUS) over 10km at 2008 Open Water World Championships.