Julian gained his PhD in 1991 from the University of Bristol through work on bacterial transcriptional regulation. He subsequently pursued postdoctoral research at the University of Birmingham on the transforming proteins of adenoviruses. He then joined the Sanger Institute in 1997 working on the genomics of major human pathogens such as Bordetella pertussis, Campylobacter jejuni, Escherichia coli, Mycobacterium tuberculosis, Neisseria meningitidis, Salmonella Typhi, Staphylococcus aureus, and many others. While at the Institute he developed genomic and experimental techniques to investigate the evolution of bacterial pathogens, their interactions with their hosts, and the evolution of resistance to antibiotics and vaccines. He joined the Department of Veterinary Medicine in 2009 to continue this, and to broaden his work on transmission of pathogens between humans and animals. He is an Honorary Professor at the University of Oxford, a Visiting Professor at the London School of Hygiene and Tropical Medicine, and was elected a Fellow of the Academy of Medical Sciences in 2009, the American Academy of Microbiology in 2012, and the Royal Society in 2014.