Fisher Funds has bought Tower Investments for $79 million, making it the fourth largest fund manager in the country and largest New Zealand-owned KiwiSaver provider.
The deal will quadruple the total funds under management by Fisher to $5.5 billion and more than double its share of the KiwiSaver market to 10%.
The deal is funded by debt and equity.
Fisher said the deal is supported by major shareholder TSB Bank.
Tower Investments will run as a stand-alone business with employees transferring with the business.
The sale will go through in early April this year and Tower will make an announcement about what it plans to do with the proceeds in due course.
The deal followed the sale of Tower's health insurance business to NIB Holdings from Australia.
Tower said on Tuesday it will focus on growing its main insurance business.
Tower's shares were unchanged at $1.90.