Christopher joined the Department of International Politics in January 2019, having previously taught History at the University of Huddersfield and Leeds Trinity University. His first monograph, entitled Civilian Specialists at War: Britain's Transport Experts and the First World War was published in April 2020 by the University of London Press as part of the New Historical Perspectives series. It was a runner up in the First Book category in the Society for Army Historical Research's annual book awards in 2021.

Christopher currently teaches on both undergraduate and postgraduate modules within the Department of International Politics, and his interests cover military logistics, the evolution of warfare in the modern era, the public image of the British Army, and global conflict. His research focuses on the intersections between the state, the military, and private enterprise, the influence of logistics on military operations, and the development of professional military education.

He has produced material for a range of scholarly and popular publications, acted as an academic consultant on the BBC2 series Railways of the Great War, and was a founding member of the First World War Network, an AHRC-funded hub for postgraduate students and early career researchers interested in any aspect of the First World War during the centenary of the conflict between 2014 and 2018.

Christopher is a Fellow of both the Royal Historical Society and the Society for Army Historical Research.

Christopher is currently the Director of Learning and Teaching within the Department, responsible for overseeing the strategic development of the learning and teaching environment and coordinating undergraduate and taught postgraduate provision.

He previously acted as Deputy Director of Undergraduate Studies within the department between September 2019 and August 2021. In this role he was responsible for chairing the undergraduate examination boards and overseeing the department's adherence to University Special Circumstances policy.