A last-ditch attempt was made in February to keep two Flaxmere ward councillors which proved the biggest sticking point in the process.
However, the commission agreed it was best to reduce that ward to one councillor.
"While the Flaxmere electoral population is clearly a distinct community of interest, it is not sufficiently large to justify two councillors under the council's proposal while also preserving reasonably fair representation for electors across the district," the determination read.
The new Māori ward will be known as the Takitimu Māori Ward.
It comes as long-standing Flaxmere ward councillor Henare O'Keefe announced earlier this year he would not be running again for council in October.
He told Hawke's Bay Today when making that announcement that losing a Flaxmere ward councillor would be his biggest regret if it went ahead.