Two years ago, people were saying Derek Nepinak had ambitions to become the National Chief of the Assembly of First Nations. Mr. Nepinak has proved them wrong.

The man who is the Grand Chief of the Assembly of Manitoba Chiefs has dismissed the AFN as an ineffective relic of a bygone era. Also dismissed by Mr. Nepinak is the Indian Act, and any laws enacted by "colonial governments" that "ride roughshod" over First Nations.

What matters, he says, are the treaties that defined the traditional territories of their native signatories and dictated the compensation to be paid for their use. Mr. Nepinak says Canada needs to live up to those deals.

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At age 39, he has emerged as a key leader of an emboldened people moving out of the shadows of the residential school system to demand their share of the wealth being reaped from a country that was once theirs alone.

"We have indigenous rights to these lands," Mr. Nepinak says, "indigenous rights that transcend, or are more fundamental, to our experience than anything that can be presumed upon us by way of the Indian Act or any other federal or provincial legislation that is written on paper."

When the AFN held its annual meeting in the Yukon last week, Mr. Nepinak organized a competing meeting on the Onion Lake First Nation in Saskatchewan, and 85 chiefs showed up – nearly half as many as there were at the AFN gathering. The discussion centred on the creation of a new organization called the National Treaty Alliance, a movement that is gathering steam even as the AFN is at risk of fracture.

Mr. Nepinak spent his early childhood living with his grandparents in the Pine Creek First Nation, where he was steeped in the culture of the Saulteaux.

His cousin, Jennifer Nepinak, said they come from a tight-knit family in which education was heavily promoted. The importance that Mr. Nepinak places on treaty rights, she said, "is just part of who we are and the way we were raised, and our values, and our view on the world overall, with the foundation being our grandparents."

Jim Kerby met Mr. Nepinak in 1989 when the two were on the same high-school football team in Airdrie, Alta. Mr. Nepinak was the starting quarterback. "We would get in a huddle and he wouldn't even have to try to take charge," said Mr. Kerby, who remains a close friend. "People listened when he talked. And he was incredibly gifted as an athlete."

Mr. Nepinak was such a good swimmer, in fact, that he tried for a spot on the Canadian Olympic team in 1992.

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After obtaining a bachelor's degree in native studies from the University of Alberta, he studied law at the University of Saskatchewan and then went to Osgoode Hall Law School in Toronto.

Paul Chartrand, one of Mr. Nepinak's professors at the University of Saskatchewan, said he and his former student found a common interest in the treaties.

"The treaties are the bargains whereby these people, the First Nations, agreed to join Canada and they've not been honoured," Prof. Chartrand said. "So it really puts in the spotlight the moral platforms of Canada because every government really has an obligation to respect the treaties and to make them effective. He [Mr. Nepinak] sees that very, very clearly. He sees the injustice of it all."

In 2009, Mr. Nepinak was called by the Pine Creek First Nation to be their chief. The reserve was in deep financial trouble, but within a year he put it back on its feet.

In 2011, he became the Grand Chief in Manitoba and quickly began to butt heads with the Conservative government in Ottawa. Mr. Nepinak was among the chiefs who tried unsuccessfully last December to force their way onto the floor of the House of Commons.

The AFN also became a target of his frustration, especially after National Chief Shawn Atleo and a small group of AFN regional representatives met with Prime Minister Stephen Harper in January over the objections of other chiefs.

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"There's a growing sense that something needs to happen – that people need an alternative," Mr. Nepinak said in April.

In June, he hopped on his motorcycle and led what he called the Treaty Freedom Caravan in a large loop around the Prairies, stopping at one First Nation after another to pitch his plan to assert First Nations sovereignty by insisting that the treaties are enforced.

Then came the Onion Lake gathering and the decision to move ahead with the National Treaty Alliance. It is unclear whether the new organization will mean the end of the AFN – or if the two groups can complement each other. What is clear is that many other First Nations leaders are prepared to follow Mr. Nepinak down that path.

"He is somebody who is a leader and is willing to make those hard decisions, those leadership decisions, and persevere despite the many obstacles that confront us," said Chief Arlen Dumas of the Mathias Colomb Cree Nation in Manitoba. "He'll take a stance and he'll stand by that stance and not make any concessions."