Family members of world-renowned Indigenous watercolourist Albert Namatjira have had the rights to his artwork returned to them, ending a struggle dating back decades.

After years of campaigning, the copyright controversy was ended not in a courtroom, but on the phone after the intervention of a high-profile Australian millionaire.

Albert Namatjira's nephew, Mervyn Rubuntja, said he was "very, very proud" to have had copyright given back to his family.

"We fought very hard for that long," he said.

"It's good [and now] it's the family's choice if they want to go ahead with [making a] copy."

Albert Namatjira died in 1959. ( Supplied: Northern Territory Library )

Dick Smith decided to offer his support to the Namatjira family's cause, after becoming convinced that there had been a "misunderstanding" between the family and copyright owner Legend Press.

"I had originally met [owner] John Brackenreg many years ago and found him to be an ethical person," Mr Smith said.

"They'd reached an impasse after about 10 years of negotiation.

"In 15 minutes, we worked our way around the problems.

"I agreed to donate some money towards the Namatjira Foundation and John Brackenreg's son Philip agreed that he'd transfer the entire copyright to the family."

Mr Smith said copyright was then handed over to the Namatjira family for a nominal amount of $1.

"I thought, this might be a chance where I could do something worthwhile, and in fact it's one of the best things I've ever been involved in," Mr Smith said.

Namatjira copyright sold by Public Trustee

Mr Namatjira died in 1959 and the Public Trustee for the Northern Territory Government took on administration of his estate, with Legend Press continuing to manage copyright and royalty payments to the Namatjira family.

But the Public Trustee sold Namatjira's copyright to Legend Press in 1983, ending the income stream to the artist's family — a decision the trustee from the time later acknowledged was wrong.

Albert Namatjira's family said they were "very, very proud" to have the copyright back. ( hermannsburgpotters.com.au )

A documentary called the Namatjira Project is being shown at the Adelaide Film Festival this week.

The film focuses on the history of the man behind the artwork, but also his family's fight to regain control over the adored watercolours.

Albert Namatjira with his father Jonathon, his wife Rubina and their grandchildren. ( Image: Courtesy of Strehlow Research Centre )

The film's producer and chair of the Namatjira Legacy Trust Sophie Marinos said she was overwhelmed by the development.

"I burst into tears — I am just so happy for the Namatjira family," she said.

"Until the final moment that it had been handed back, I never thought it would happen.

"I really do hope that, on the ground, it does see real benefits for them, and their children, and grandchildren going forward, because that is really what they dream of."