The situation was altered in 1846, however, when the New Zealand Constitution Act 1846, divided the colony into two provinces and provided each with its own political institutions in addition to the central government at Auckland. The two provinces were called New Ulster and New Munster, New Leinster being merged with the South Island and the southern portion of the North Island up to the mouth of the Patea River, to form the new New Munster. Each province was provided with a Governor and Legislative and Executive Council, in addition to the Governor-in-Chief and Legislative and Executive Council for the whole colony. Early in 1848 Edward John Eyre was appointed as Lieutenant-Governor of New Munster. In 1851 the Provincial Legislative Councils were permitted to be partially elective.
The Provincial Council of New Munster had only one legislative session – in 1849 – before it succumbed to the virulent attacks of the Wellington settlers. Governor George Edward Grey, sensible to the pressures, inspired an ordinance of the General Legislative Council under which new Legislative Councils would be established in each province with two-thirds of their members elected on a generous franchise. Grey, however, proceeded to implement the ordinance with such deliberation that neither Council met before advice was received that the Parliament at Westminster had passed the New Zealand Constitution Act 1852.
The province was dissolved after only seven years in 1853, with the New Zealand Constitution Act 1852, abandoning both the nomenclature and the boundaries of these provincial divisions, and New Munster was divided into the provinces of Canterbury, Nelson, and Otago. From that date onwards New Munster, like New Ulster and New Leinster, disappeared from the New Zealand scene and became of historical significance only.