The Act begins with a preamble that declares that the three provinces New Brunswick, Nova Scotia and the Province of Canada (which would become Ontario and Quebec) have requested to form "one Dominion...with a Constitution similar in Principle to that of the United Kingdom". This description of the Constitution has proven important in its interpretation. As Peter Hogg wrote in Constitutional Law of Canada, some have argued that since the United Kingdom had some freedom of expression in 1867, the preamble extended this right to Canada even before the enactment of the Canadian Charter of Rights and Freedoms in 1982; this was a supposed basis for the Implied Bill of Rights. In New Brunswick Broadcasting Co. v. Nova Scotia, the leading Canadian case on parliamentary privilege, the Supreme Court of Canada grounded its 1993 decision on the preamble. Moreover, since the UK had a tradition of judicial independence, the Supreme Court ruled in the Provincial Judges Reference of 1997 that the preamble shows judicial independence in Canada is constitutionally guaranteed. Political scientist Rand Dyck has criticized the preamble, saying it is "seriously out of date". He claims the Constitution Act, 1867 "lacks an inspirational introduction".
The preamble to the Constitution Act, 1867 is not the Constitution of Canada's only preamble. The Charter also has a preamble.
Part I consists of just two sections. Section 1 gives the short title of the law as The British North America Act, 1867. Section 2 indicates that all references to the Queen (then Victoria) equally apply to all her heirs and successors.
The British North America Act, 1867 established the Dominion of Canada by fusing the North American British "Provinces" (colonies) of Canada, New Brunswick, and Nova Scotia. Section 3 establishes that the union would take effect within six months of passage of the Act, and Section 4 confirmed that "Canada" was the name of the new country (and the word "Canada" in the rest of act refers to new federation and not the old province).
Section 5 lists the four provinces of the new federation. These are formed by dividing the former Province of Canada, into two; its two subdivisions, Canada West and Canada East, were renamed Ontario and Quebec, respectively, and became full provinces in Section 6. Section 7 confirms that the boundaries of Nova Scotia and New Brunswick were not changed. And Section 8 provides that a national census of all provinces must be held every ten years.