During his Ministry of Defence (MoD) career he occupied a wide range of analytical and management positions in the DIS and elsewhere, including three tours in the Cabinet Office, culminating as Secretary to the Joint Intelligence Committee (JIC).
During this period he represented the MoD and DIS as a member of the JIC, UK representative to the NATO Intelligence Board and Head of Profession for MoD Intelligence Analyst classes.
On leaving the DIS and the civil service in 1999, Morrison was selected by the parliamentary Intelligence and Security Committee (ISC) to be its first Investigator.
Morrison is a joint author of The Open Side of Secrecy: Britain's Intelligence and Security Committee, the first in-depth study of the ISC.
Since his retirement, Morrison has appeared on a number of TV and radio programmes, including Panorama, Today, The Politics Show, Newsnight, and Conspiracy Files (on the death of Dr David Kelly).