James Down made his senior debut for Llantwit Fardre before being called-up to train with Cardiff RFC in the summer of 2006. 

Having progressed through the Cardiff Blues Academy, Down made his senior debut for the region against the Borders in January 2007.

Having progressed well, Down showed the potential he had over the next few seasons, but suffered a horrific broken leg when he fell at the tackle area in the second minute during the Racing Metro v Cardiff Blues match in Paris in November 2011. 

Down made his 100th Cardiff Blues appearance in the 2016 Boxing Day derby against Dragons at Cardiff Arms Park.