Yes, Māori ceded sovereignty to the British Crown in the Treaty of Waitangi.

In the Māori text of the Treaty, which was the version most chiefs signed, the key term is kawanatanga (governorship), was used to describe what Māori were ceding to the Crown. While some argue this term may have implied limited governance, contemporary Māori signatories, missionaries, and the Crown understood it to mean the transfer of governance to the British Crown. The English draft explicitly refers to the "cession of sovereignty."

Governor Hobson clearly interpreted the Treaty as a full cession of sovereignty, which was affirmed in subsequent declarations and actions. The Māori signatories were promised the protection of their rangatiratanga (chiefly authority) over their lands and property, but within the framework of British sovereignty.

The 1877 Wi Parata case described the Treaty as a “simple nullity” in domestic law, but in practice, the Crown acted from the outset on the basis that sovereignty had been ceded. More recently, however, some academics and the Waitangi Tribunal (in its 2014 report on the Northland inquiry, Wai 1040) have controversially claimed that Māori did not intend to cede sovereignty. This view contradicts earlier legal and historical interpretations.

References:

• https://sites.google.com/site/treaty4dummies/home/treaty-of-waitangi
• Wi Parata v Bishop of Wellington (1877) 3 NZ Jur (NS) SC 72