A man convicted of murder after torching an occupied house in 1999 was today granted a retrial by the Supreme Court.

The ruling came after the court found errors in a judge's original trial summary.

Aerengaroa Timoti, then 23, was convicted in the High Court at Auckland for setting fire to his mother's Mt Roskill house while five people were inside.

He pleaded guilty to arson, was acquitted on two attempted murder charges, but was found guilty of the murder of Tereoro Ruarau, the only occupant who didn't manage to escape the petrol-fuelled blaze.

Timoti appealed the conviction but it was dismissed by the Court of Appeal.

He later appealed to the Supreme Court after a landmark Privy Council decision criticised the Court of Appeal for refusing him legal aid, saying it breached the Bill of Rights Act.

The Supreme Court finding said that in light of evidence from the initial trial, the jury could reasonably conclude that two of the home's occupants had provoked Timoti.

In a 25-page report the Supreme Court supported arguments from defence lawyer Greg King regarding provocation and self-control legalities.

The 1999 incident was the result of ongoing tensions in the home between Timoti and his mother and step-father involving money and personal matters surrounding Timoti's infant child.

The Supreme Court concluded that the provocation from the pair toward Timoti before he doused the house in petrol and lit it was significant.

Mr King had outlined Timoti's vulnerability to such provocation.

The Supreme Court report said the provocation was "sufficient to deprive a person having the power of self-control of an ordinary person, but otherwise having the characteristics of the accused..."

The Court of Appeal maintained Timoti must have known someone was likely to be killed by his actions, meaning there was murderous intent.

However, the Supreme Court concluded there were several errors in directions given to the jury during the judge's summary of the case, and those misdirections may have deprived Timoti of a manslaughter verdict.

The court set aside the conviction -- for which Timoti is serving a life sentence -- and directed a new trial.