The deal will see Co-op Money become part of NZCU Baywide, but the organisation will retain its name, the firms said in a statement.
The acquisition is the latest transformation for NZCU Baywide, which consolidated four credit unions under Credit Union Baywide in May.
NZCU Baywide now has more than $500 million in assets, and roughly 300 staff.
Gavin Earle, chief executive of Baywide, said the deal paved the way for further change in the credit union sector.
“Our sector is an incredibly important part of New Zealand’s financial heritage. Just like any other part of the financial sector, it’s constantly under pressure to evolve, adapt and be more efficient.
“This acquisition helps us do this while also achieving more agility to respond to customer needs – we have to be the absolute best we can be at serving our member-owners.
“As the largest New Zealand credit union we are in a strong position to achieve this outcome," Earle added.
Under the terms of the agreement the existing credit unions and third party customers of Co-op Money NZ will continue to receive services from Co-op Money NZ, the companies said.