He was awarded the Bradman Young Cricketer of the Year at the Allan Border Medal ceremony by the CA in 2005.

Later in 2007 he declined an offer to return to Glamorgan, instead joining the Centre of Excellence in Australia at the request of national chairman of selectors Andrew Hilditch.

Jamie Cox, the state's director of cricket, said that "we were unable to help him fulfil his full potential."

He had scored 511 first-class runs in 2009–10, including two hundreds, and also averaged more than 40 in the one-day competition while also playing as South Australia progressed to the Twenty20 domestic final.

In 2012-13 Cosgrove scored 784 runs at 39.20 in the Sheffield Shield, the second-highest total in the competition behind Tasmanian teammate Ricky Ponting.