The roles and responsibilities of Canada’s Chief Medical Officers of Health (CMOHs) are contested. On the one hand, they are senior public servants who confidentially advise government on public health matters and manage the implementation of government priorities. On the other hand, CMOHs are perceived as independent communicators and advocates for public health. This article analyzes public health legislation across Canada that governs the CMOH role. Our legal analysis reveals that the presence and degree of advisory, communication, and management roles for the CMOH vary considerably across the country. In many jurisdictions, the power and authority of the CMOH is not clearly defined in legislation. This creates great potential for confusion and conflict, particularly with respect to CMOHs’ authority to act as public health advocates. We call on governments to clarify their preferences when it comes to the CMOH role and either amend the relevant statute or otherwise find ways to clarify the mandate of their CMOHs.