Dion received his degree in Medicine from Bristol University in 1985. He was given an honorary consultant appointment at the University Hospital Birmingham in 1996, and was appointed Professor of Surgery in 2006.
He is Director of the Birmingham Experimental Cancer Medicine Centre, Director of Clinical Research at the Royal College of Surgeons of England since October 2011 and Deputy Head (Clinical) at the School of Cancer Sciences since December 2012. He is also Research Committee Chair at the European Society of Coloproctology.
His research interests are predominantly in clinical and translational research in colorectal cancer, but also encompassing the development of clinical trials in surgery