James Cook commissioned into the Royal Regiment of Artillery in December 1995. He has served the majority of his regimental duty within 29 Commando Regiment, and commanded 105th Regiment Royal Artillery, based in Edinburgh. 

At staff he is a qualified Gunnery Instructor and ISTAR Officer as well as completing the Combat Arms Fighting Systems course at the Royal College of Military Sciences in 1999. He has instructed phase two soldiers and been a Company Commander at the Royal Military Academy Sandhurst. 

In the General Staff he has been Assistant Head Concepts in the Army HQ focusing on the future of warfare, Assistant Head General Staff in the Army Personnel Centre, and is now Director Programme CASTLE looking into the future of talent management. 
 
Brigadier James is the Chairman of the Army Rugby Union and represents the Army’s view on the RFU Council at Twickenham. In 2022 he was appointed to the Board of the RFU, responsible for all rugby matters in England. In November 2016 he was appointed OBE for services to Army sport. He is the Chair of the Royal Artillery Historical Committee. Chair of the Governors of John Hanson School and Chair of the Parent Teacher Association of Portway school. 

He completed his PhD in 2020 on how the British Army transformed in the First World War.