The Secretariat has a dual mandate: To support the Treasury Board as a committee of ministers and to fulfil the statutory responsibilities of a central government agency. This entails providing operational programs to carry out the legislated responsibilities of the Treasury Board. These responsibilities derive from the broad authority of sections 5 - 13 of the Financial Administration Act, as well as the authorities in other Acts, including: The Public Service Labour Relations Act, the Employment Equity Act, the Official Languages Act, the Access to Information Act, the Privacy Act, the Federal Real Property and Federal Immovable Act, and the Public Service Employment Act. The Secretariat's responsibilities for the general management of the government cross all policy sectors managed by 22 operating departments and many other organizational entities as reported in the Main Estimates.

The role of the Secretariat is to define and develop modern governance at the federal level. Although the accountability for Public Service management increasingly rests with departments, the Treasury Board of Canada and its Secretariat provide strategic leadership in Public Service management and reform through a management board role. That role emphasises results-based management and facilitation, essential central controls, and intervention when necessary.

The mission of the Secretariat is to support the Treasury Board and to help the Government of Canada operate effectively within available resources. The Secretariat implements the policies developed by the Treasury Board as the manager of the Public Service and manages the human, financial, information technology, and material resources that support it. This is carried out by several branches/sectors of the Secretariat, described below under "Organization".