In any country where there are state or provincial governments as well as a central government, there are bound to be occasions where conflicting or contradictory laws are passed by a state or provincial government, on the one hand, and the central government on the other. Each country (or federation) must find a way to resolve or reconcile these contradictory enactments. In Canada, as a result of decisions made by our courts over the years, we have adopted the notion of federal paramountcy to resolve these conflicts. That is, when federal and provincial laws cover the same or similar subject matters, and there is a conflict between those laws, the central law is operative and the provincial law (to the extent of the conflict) is rendered inoperative. In other words, the provincial law remains valid but cannot operate so long as the central or federal law occupies the field.
The issue of paramountcy, however, is dependent upon a preliminary determination that both the federal and provincial laws are constitutionally valid under the respective jurisdictions of Parliament and the legislatures under the Constitution Act, 1867.
Over the years, different theories have emerged as to when the ‘doctrine of paramountcy’ arises. Some courts and some writers have theorized that paramountcy arises when similar federal and provincial laws merely co-exist. Others have felt that an actual conflict is necessary between federal and provincial laws where obedience to one law requires disobedience to the other before paramountcy arises. Some courts and some writers have made distinctions among three scenarios: first, there is the situation where provincial laws have merely supplemented federal laws; second, there is the case of provincial laws that are duplicative of federal laws; and finally, there are provincial laws that actually conflict with federal laws. However, the Supreme Court of Canada has resolved the matter by concluding that there must be an operational incompatibility or operational inconsistency between the federal and provincial laws before paramountcy arises (see Smith v. The Queen,  S.C.R. 776). That is, the courts now say that there must be an actual conflict between federal and provincial laws before the ‘doctrine of paramountcy’ is triggered, and then, the provincial law will be held to be inoperative only to the extent of the conflict or operational incompatibility or operational inconsistency.
In addition to the foregoing, there are two instances in the Constitution Act, 1867 where paramountcy is explicitly recognized. The first is section 94A, which is concerned with old age pensions and supplementary benefits. Both Parliament and the legislatures are given concurrent jurisdiction over those matters but no federal law “shall affect the operation” of any provincial law dealing with those matters – in effect, a recognition of provincial paramountcy in respect of laws providing for old age pensions and supplementary benefits. The second instance is section 95 where Parliament and the provincial legislatures are given concurrent jurisdiction over agriculture and immigration. However, section 95 provides that a provincial law dealing with agriculture or immigration shall only have effect “as long and as far only as it is not repugnant “ to a federal law dealing with those matters. Notwithstanding the particular references to paramountcy in sections 94A and 95, the general rule, set out by the courts, is that of federal paramountcy as described above.