Justin originally trained in medicine at Trinity College Oxford, where he gained a first class degree. He completed junior doctor there then an internal medicine residency at The Johns Hopkins Hospital in Baltimore, returning to continue his career at The Royal Marsden and then St Bartholomew's Hospitals. His PhD research investigated the interplay between the immune system and cancer; he was appointed a senior lecturer in 2007, and a Professor in 2009.

Professor Stebbing has published over 650 peer-reviewed papers. His focus at ARU, Cambridge (Professor of Biomedical Sciences ) and Imperial, London (Visting Professor of Oncology) is on new therapies in cancer, and the systemic management of patients with solid malignancies including a number of new biomarker-based approaches. The charity Action Against Cancer www.aacancer.org has been set up to support Justin's work which concentrates on drug development, gene regulation and has the ambitious goal of developing cures.

He sits on a number of international cancer committees.  Justin's team published in Nature Medicine the discovery of a new cancer-causing gene (LMTK3) which we have now implicated in breast, gastro-intestinal, lung and other solid tumours. The National Institute for Health Research (NIHR) awarded Justin Stebbing its first translational research professorship in oncology, aiming to bridge the gap between the laboratory and the patient to ensure therapy is personalised. The focus of this is understanding why some patients with cancer relapse, and developing a program to reverse this and prevent it.

The National Institute for Health Research (NIHR) awarded Justin its first translational research professorship in oncology, aiming to bridge the gap between the laboratory and the patient to ensure therapy is personalised. During the COVID-19 pandemic, papers published by Justin described use of artificial intelligence to find a new treatment, leading to mechanistic and clinical studies for baricitinib and then its FDA approval. In randomised studies, it has the largest mortality benefit for any drug to treat hospitalised patients with COVID-19 and the WHO has placed it at the top of its evidence hierarchy. This simple once/daily tablet has saved thousands of lives and it lends itself for use in low- and middle-income countries.

In 2016 Justin became Editor-in-Chief of Oncogene (Nature Publishing Group's cancer journal) and was elected to the American Society for Clinical Investigation.