Simon James read archaeology at the London Institute of Archaeology, where he also took his PhD, by which time the Institute had become part of University College, London. He moved to the British Museum, first as an archaeological illustrator and then as a museum educator, responsible for programmes relating to the later prehistoric and Roman collections. After a decade at the British Museum, he decided to seek a career in research and teaching. Having held a Leverhulme Special Research Fellowship at the University of Durham, he joined the School in January 2000, was promoted Senior Lecturer in 2002, and Reader in 2005. In April 2012 he was awarded a personal chair. He was the School's Director of Research 2012-14.
He is a member of the University of Leicester-based team conducting the Leverhulme Trust-funded research programme on the Impact of Diasporas on the Making of Britain. From 2010 to summer 2012 he was on research leave, substantially funded by the Leverhulme Trust, studying the Roman military base at Dura-Europos, Syria. His previous work on the military archaeology of Dura included identification of probable use of 'chemical warfare' during the final siege of the city c.AD256.
He is also now coordinating the School's involvement in excavations near Caerwent as part of the tri-Service Operation Nightingale, providing archaeological fieldwork opportunities to help injured soldiers in their recovery, and is now academic advisor to the UK's tri-Service Defence Archaeology Group.
In 2012 Simon was invited to become President of the Ermine Street Guard.