Hawaiki owns and operates the Hawaiki Transpacific Cable which went into operation in July 2018, and spans 15,000km.
It is claimed to be the fastest and largest capacity link between New Zealand, Australia, Hawaii and mainland US, with a design capacity of 67Tbps.
In a statement, Hawaiki executive chairman Remi Galasso said: ""We are delighted to welcome BW Group as a shareholder. Having established a successful subsea cable business with the support of our customers and partners, the company started a process to find a new long-term shareholder who is able to take the company to the next stage of development.
"Three years after Hawaiki's commercial launch, it is time to write a new chapter of the company's history and we believe BW is an ideal shareholder for this fast-growing business."
There will be no change in the personnel who manage the Hawaiki business.
BW Group executive chairman Andreas Sohmen-Pao said: "We are excited to be making this investment in Hawaiki's outstanding platform and team.
"BW Group has a deep heritage in maritime connectivity and infrastructure, with assets spanning production, transportation and distribution.
"Our strategy is to help connect countries across the oceans while working to reduce our environmental impact, including recent investments into wind installation vessels, floating wind, batteries, solar and other sustainable technologies.
"Hawaiki is a great fit and we are pleased to be able to support the team in their next phase of development."