Professor David Dearnaley joined the Academic Unit of Radiotherapy at The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research, London, as Bob Champion Senior Lecturer and Honorary Consultant in 1987. He subsequently became Reader in Prostate Cancer Studies in 1999 and Professor of Uro-Oncology in 2003.

He was Head of The Royal Marsden Urology Unit from 1994 to 2006 and Chairman of The Royal Marsden and ICR Committee for Clinical Research 2006–13. He was the Prostate Theme Lead for The Royal Marsden/ICR Biomedical Research Centre until April 2017. He was appointed an NIHR Senior Investigator in 2008 and is a member of the NHS R&D HTA Clinical Trials Board College of Experts (2012-). He has previously chaired both the MRC and NCRI Prostate Study Groups, as well as the MRC Radiotherapy Clinical Trials Group.