New Zealand Superannuation Fund is taking a 41 percent cornerstone stake in locally-owned life insurer Fidelity Life for $100 million.
The conditional agreement values Fidelity at between $198m and $220m, and gives the insurance company the capital it needs to expand.
Super Fund chief investment officer Matt Whineray said in a statement it was a good move.
"This is a rare opportunity for the Fund to take a significant direct stake in a New Zealand life insurance company. The additional capital we are providing will support Fidelity's long-term growth plans," he said.
Mr Whineray declined any further comment ahead of Fidelity's shareholders voting on the deal in mid-December.
Fidelity Life chief executive Nadine Tereora said the company's resources could not keep pace with its rapid growth.
"I think it is a brilliant 'New Zealand Inc.' story, where you've got two New Zealand-focused businesses partnering up to drive future growth in a really important sector," she said.
If approved, the Super Fund will get $75m of new shares in Fidelity at an issue price of $115 each, and will buy another $25m of existing shares.