In the Court of Appeal at Auckland, Popata's lawyer Louise Freyer said he was not present during the initial robbery and assault, and arrived on the scene shortly afterwards.
Mrs Freyer said at Popata's sentencing, Judge Nevin Dawson relied on a Crown summary prepared before the trial, rather than the evidence that came out at the trial. This meant Popata received a harsher sentence than he should have.
It was an unusual situation as Judge Graham Hubble oversaw the trial and then retired straight after, so Judge Dawson took over the sentencing.
Mrs Freyer said Popata should be re-sentenced, and the Court of Appeal judges, Justices Pamela Andrews, Patrick Keane and Lynton Stevens, agreed.
They quashed his sentence and sent the matter back to the district court for re-sentence on a date yet to be set.
Popata's home detention term was suspended after two weeks to allow his appeal to be heard.
In 2009 he was convicted for assaulting Mr Key outside Te Tii Marae by pulling his jacket and sentenced to 100 hours' community work.
A year later Popata led Ngati Kahu protesters in an occupation of a Far North District Council-owned reserve.