Formerly, the position of principal secretary was the most senior one in the Canadian Prime Minister's office (PMO).
The role of the principal secretary may vary, depending on how the prime minister or premier structures the workflow in their office.
This has sometimes led to ambiguity in clearly defining the distinction between the roles of principal secretary and chief of staff to the general public.
Depending on the personal approach of the Prime Minister, the duties of managing, administrating and co-ordinating the activities of the PMO may belong to the Principal Secretary, the Chief of Staff, or another key advisor.
The Government of Canada does not maintain an official, complete list of persons that have held leadership positions in the PMO.