In Canada, the principal secretary is a senior aide, often the most senior political aide, to a head of government. Formerly, the position of principal secretary was the most senior one in the Canadian prime minister's office (PMO). However, since 1987, it has been second to the chief of staff position. The leader of the official opposition and most Canadian provincial premiers also have a principal secretary. The role of the principal secretary may vary from administration to administration, depending on how the prime minister or provincial premier structures the workflow in his or her 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.

List of principal secretaries to the prime minister