While Te Reo Māori is the primary language, many Māori people are also fluent in English, the official language of New Zealand. In fact, a significant number of Māori speak both languages fluently, making them bilingual.
It's also worth noting that there are various dialects of Te Reo Māori, depending on the region of New Zealand.
So, to answer your question directly: The main language spoken by Māori is Te Reo Māori, and many also speak English.