Gina Rinehart's eldest daughter Bianca has been handed control of the family's trust worth more than $4 billion.

The NSW Supreme Court in Sydney appointed Ms Rinehart as trustee following the family's long-running legal battle.

Justice Paul Brereton said Ms Rinehart had demonstrated the ability to robustly assert the rights of the trust over her mother and her company Hancock Prospecting.

He found she was better suited than any of the alternatives to administer the trust under the circumstances.

He ordered her mother to deliver the trust documents to her eldest daughter.

In handing down his decision, Justice Brereton said it had become clear throughout the proceedings that Mrs Rinehart had "gone to extraordinary lengths" to maintain control directly or indirectly of the trust.

And he said she had exerted "enormous pressure and great influence to do so".

He said it was a reasonable inference that she would try to influence any trustee who tried to move against her interests.

Some of Mrs Rinehart's children originally claimed she engaged in misconduct by changing the date they could access their money without telling them.

In June 2014, Mrs Rinehart indicated she wanted to be removed as the trustee of the Hope Margaret Hancock Trust but wanted mediation to decide who should replace her.

However, two of her children, John Hancock and Ms Rinehart, pushed ahead with court action.

Hope Rinehart Welker, who initially supported Mr Hancock and Ms Rinehart, withdrew from action in early 2014.

Ginia Rinehart was the only one of the children who supported her mother.

Justice Brereton said any objections she had in her older sister taking over the trust had not been presented.

In favour of Mrs Rinehart, the court dismissed a claim that certain amendments to the constitution of Hancock Prospecting in 2006 had been improperly agreed to by Mrs Rinehart.

It was deliberated whether the amendments should be declared ineffective on the ground that Mrs Rinehart's consent to them was a "fraud of power", but the challenge was rejected by the court.

After the judgement was handed down, a Hancock Prospecting spokesman welcomed that aspect of the decision in a statement on behalf of the company.

"The company is pleased that the challenge to the amendments to its constitution have been rejected and that those amendments remain valid," he said.

"We note that the trustee will be required to consult with all beneficiaries and get the advice of the court."

Lawyer and confidante believes family will reconcile

Lawyer Alan Camp has known and worked with the Rinehart family for more than 40 years, starting with Lang Hancock, then Gina Rinehart, and is now a confidante to John Hancock and Bianca Rinehart.

He told the ABC's 7.30 program that Justice Brereton found a long list of misconduct against Mrs Rinehart.

"Findings against Mrs Rinehart that first of all, went to her manipulation of advice offered initially by PricewaterhouseCoopers which she then prevailed on them to change and they agreed somehow to change," he said.

"He found that she had deployed people including Barnaby Joyce and others to bring pressure to bear or attempt to bring pressure to bear on one of her younger children Hope, who later pulled out of the case.

"One notable example was just before Bianca gave her evidence, the night before, she'd prevailed on Grant Hackett to send Bianca an email bringing pressure to bear on Bianca, which he didn't do, but that was the pressure she tried to bring to bear and the judge found that it was conduct that he'd never experienced before.

But Mr Camp said he believed the family would eventually be reconciled.

"They are all very robust individuals and once resolved everything will be resolved," he said.

"It'll take time but John and Bianca are very understanding people.

"They know what's got to be done but they also know all the emotions that's involved and they have considerable care towards their mother."

ABC/AAP