Māori Development Minister Willie Jackson has paid tribute to his uncle the late Moana Jackson, just days after the Labour Minister's mum Dame June Jackson died.

Prime Minister Jacinda Ardern has also addressed the highly-respected lawyer, scholar and activist's passing, saying he had "left a mark on an entire generation".

Jackson died after battling a long-term illness. His death followed a record of fierce advocacy for Māori, reforming the criminal justice system and dismantling racist structures.

Jackson (Ngāti Kahungungu, Ngāti Porou, Rongomaiwahine), navigated both worlds of te ao Māori and te ao Pākehā, bringing with him immense knowledge to overthrow the negative impacts of colonisation.

Prime Minister Jacinda Ardern said Moana Jackson had inspired a generation. Photo / Mark Mitchell

"To have two great leaders lost in the Jackson whānau in such a short space of time is just devastating," Ardern said today, also referring to Dame June Jackson, who died on Monday.

"Moana Jackson was well-known domestically and internationally for his expertise in indigenous issues.

"He was incredibly generous with his time and sharing of his knowledge, storytelling and gentle approach.

"He will have left a mark on an entire generation and beyond."

Asked about his impact in the field of co-governance, which has recently been brought back into the political landscape, Ardern said he had left a legacy.

"His legacy will come down to all of us. We can do things differently and can recognise and fulfil the responsibilities we have to one another in a way that is unique to New Zealand, and we don't need to be afraid of that."

Willie Jackson told the Herald his uncle was "articulate" but without needing to raise his voice.

"Uncle could dismantle any argument. He was one of the most brilliant minds I have ever known. I saw him dismantle Gerry Brownlee once."

Jackson was described as similar to his brother Syd Jackson, a prominent Māori activist and trade unionist of the 1980s and 1990s.

"Uncle Moana was a man who always waited to be called on and was never one to jump in front of the limelight," Willie Jackson said.

The past fortnight has been tough for him with the death of close friend Wira Gardiner, his mother and now his uncle.

"I was proud to have an uncle held in such high esteem and who had such a brilliant mind."

Jackson was also an author and lecturer who specialised in the Treaty of Waitangi and constitutional issues.

He graduated in law and criminology at Victoria University of Wellington, then later taught te reo Māori.

He went on to further his studies in the United States before returning to New Zealand to conduct research for the then Justice Department report on the Māori and the criminal justice system, He Whaipaanga Hou.

He contributed a lot of his training and work towards international indigenous issues, including the United Nations Declaration on the Rights of Indigenous Peoples.

He was a judge on the International Tribunal of Indigenous Rights in Hawaii in 1993, and again in Canada in 1995.

Jackson was recognised as a respected vocal critic for Māori issues, particularly during the time of the government's foreshore and seabed legislation in 2004.

He was also vocal towards the October 2007 police "terror" raids. He resigned as patron of the Police Recruit Wing 244 due to his opposition to how the raids were conducted which he said stemmed from racism.

He was heavily involved in work around constitutional reform and Te Tiriti, producing the Matike Mai report in 2016 with Professor Margaret Mutu, based on hundreds of hui across the motu, outlining a vision for constitutional transformation in Aotearoa.

By 2040, it called for a new political system with Māori and the government sharing power, resources and responsibility for resources and social policy.

Civil Defence Minister Kiritapu Allan, who was mentored by Jackson as a young lawyer, said he would be not only "missed as a son of Ngāti Kahungungu but as one of New Zealand's finest judicial thinkers".

Asked about progress in areas he had been advocating including justice where Māori remain disproportionately impacted, Allan said some of those visions around equity were resonating now.

"He was a visionary and I think we are starting to see some of those resonate now. The Māori Health Authority is focused on equity... in justice he had just finished working on the report Ināia Tonu Nei – Hui... [Corrections Minister] Kelvin Davis is doing transformative work on the back of that."

Allan said he would always push the Government and particularly Māori MPs to always remember "our people need you to be focused".

"His words would be ringing in our ears".

Treaty Negotiations Minister and former justice minister Andrew Little said Jackson was a "real tower of strength in advocacy for Treaty compliance Treaty rights".

"But actually just for a fair and better justice system, and he will be very, very sorely missed."

Green Party co-leader Marama Davidson said Jackson had impacted not only Māori but the whole of Aotearoa.

"Moana was a mentor to so many across the motu. He bravely challenged structural and institutional racism, advocating for an Aotearoa that was decolonised and re-indigenised.

"Moana always spoke not just truth to power, but truth about our power as Māori because he knew what was right for Māori, was right for everyone."

As an activist herself, Davidson said Jackson had helped her over the years, particularly around challenging racism.

His legacy would live on "in the many generations of people who endeavour to continue the kaupapa of decolonising our country", she said.

Te Pāti Māori co-leader Rawiri Waititi tweeted Jackson was a "man of great mana and even greater humility".

"An intellect that is second to none and an unwavering commitment to constitutional transformation underpinned by Te Tiriti o Waitangi.

"Aotearoa is poorer for your departure, Moana."