The Privy Council in London says the Teina Pora case was one of two key cases to come before it in the past six months.
Pora has served 21 years in prison for the rape and murder of Susan Burdett but he maintains his innocence.
The Privy Council, which hears cases from 27 countries, heard Pora's appeal against his convictions in November.
It reserved its decision and is expected to release it early this year.
The council said the Pora case was likely to be the last appeal from New Zealand, where the law allowing appeals to the council was changed in 2003.
Only cases predating that can be considered.