The General Assembly for the colony was to consist of the Governor, a Legislative Council, and a House of Representatives. The Council was to be a nominated body, and the House was to be elected. The electoral franchise appeared to be almost universal, in that there was no racial distinction and a not very onerous property qualification, but the Maoris were in practice disfranchised because of their communal system of land owning. In each of the provinces there was to be a superintendent and a provincial council of at least nine members. The superintendent and members of the council were to be elected under the same franchise as that for the House of Representatives.

The Assembly would be competent to make laws for the peace, order, and good government of New Zealand, provided those laws were not repugnant to the law of England. The legislative competence of the provincial councils was stated in similarly wide terms, but certain specific topics were reserved to the General Assembly, which was also to have the authority to supersede provincial legislation. Since, therefore, the provincial councils had no exclusive lawmaking powers, the Constitution could not be regarded as establishing a federal system.

After some delay in the calling of the General Assembly, it met for its first session in May 1854. This first session was primarily concerned with the one matter which, although the main objective of the colonists, was not mentioned either in the Constitution or in the accompanying instructions: responsible government. As the position stood immediately before the enactment of the 1852 Act, the Executive Council consisted of Crown servants who were responsible to the Crown. In the absence of any indication to the contrary, Colonel Wynyard, who was by 1854 administering the Government, was of the view that he could not appoint an executive responsible to Parliament until he received instructions from London. Moreover, according to his Attorney-General, he had no authority to dismiss the official members of his Executive Council.

A compromise resulted from an almost unanimous resolution affirming the principle of the responsible executive. Three members of the House of Representatives and, later, one from the Legislative Council were added to the Executive Council as ministers without portfolio. The unofficial members soon found it necessary to withdraw, and it was not until another attempt to establish a mixed Executive Council had failed that Colonel Wynyard received advice from London that responsible government could be introduced without legislation and that he could accept a responsible ministry if adequate pensions were provided for the deposed official members. An election followed, and after the second Parliament assembled in 1856 legislation providing for pensions for the official members was passed and Governor Sir Thomas Gore-Browne asked Henry Sewell to form the first responsible ministry.

Canada provided the prototype for the establishment of responsible government. There Lord Durham had suggested that the Colonial Governor should act on the advice of ministers who could command a majority in the Colonial Assembly except in matters that directly involved “the relations between the mother country and the Colony”. Durham defined these “imperial issues” as being constitutional amendments, foreign relations, external trade, and the disposal of public lands. Governor Gore Browne evidently had these issues in mind when he obtained Sewell's signature to a minute in which the Governor retained his authority “On matters affecting the Queen's prerogative and imperial interests generally …”. The minute continued: “Among imperial subjects the Governor includes all dealings with the native tribes, more especially in the negotiation of purchases of land…. The Governor alone is responsible to Her Majesty for the tranquillity of the Colony….”. The reference to dealings with the Maoris reflected conditions in New Zealand. The Constitution Act had already reserved the purchase of Maori land to the Governor and in other ways ensured that Maori policy and its administration would remain in the hands of officers responsible to the Governor. Nevertheless, the sale of land once acquired by the Crown was to be at the disposal of the General Assembly – a significant concession because the sale of land was an important source of revenue.