Ngāi Tahu plans to leave the South Island network of Whānau Ora providers, taking on responsibility for services that are specific to its people.
Ngāi Tahu joined Te Pūtahitanga o Te Waipounamu with eight other South Island iwi in 2014 to provide health and social support services to whānau Māori.
Iwi kaiwhakahaere Lisa Tumahai said the decision for the iwi to leave was not easy.
"This move in a new direction for Ngāi Tahu is something that Te Rūnanga o Ngāi Tahu has put a great deal of careful thought into," she said in a statement.
Ngāi Tahu said it now had the capability to partner with the Crown itself, to exercise its own rangatiratanga with its own services for whānau.
"We are taking responsibility for the wellbeing of our own whānau and hapū by continuing our focus on self-determination which has anchored Ngāi Tahu for generations," Tumahai said.
Ngāi Tahu will continue to support Whānau Ora for pan-tribal services, and Te Pūtahitanga o Te Waipounamu will continue as the South Island commissioning agency.
"We acknowledge the work of Te Pūtahitanga in supporting our whānau. We strongly believe that now is the right time for us to directly fulfil the goals and aspirations of Ngāi Tahu whānau," Tumahai said.
Te Taumata co-chairs Gena Moses-Te Kani and Dr Taku Parai said in a statement they had enjoyed eight years of partnership with Ngāi Tahu and looked forward to working together in other ways to support whānau.
"The creation of Te Pūtahitanga o Te Waipounamu was truly groundbreaking, bringing together nine iwi in the spirit of partnership and kotahitanga to deliver Whānau Ora across the South Island," Moses-Te Kani said.
"We still share the same goals when it comes to creating better outcomes for whānau Māori, and wish them the very best as they follow their own strategic direction," Parai said.
Since its settlement in 1998, Ngāi Tahu has spent more than $650 million helping address social and economic inequalities for its people.