The owner of the TSB Bank is taking over the investment manager Fisher Funds but is keeping the same management and bringing in a partner.
The TSB Community Trust has exercised an option to buy the 51 percent of Fishers it didn't already own for an undisclosed sum.
It will sell a near 25 percent stake in Fisher to a United States private equity company, TA Associates.
That stake will increase to 34 percent after it gets the necessary regulatory approvals.
TSB has had a stake in Fisher since 2013, and increased its initial 26 percent stake to 49 percent two years ago, with an option to acquire the rest.
Fisher Funds is New Zealand's fifth-largest fund manager, with more than 270,000 clients and $7 billion of funds under management.
TSB Group chair Hayden Wano said it was looking for ways to expand Fisher Funds.
"That's probably a discussion that will come out from the boardroom in an appropriate time," he said.
Mr Wano said TA Associates provides experience and expertise to the venture.