Crown-owned company Reannz has signed a deal to buy $65 million of capacity on the proposed Hawaiki cable that would link New Zealand, Australia and the United States.
Reannz operates a high-speed research network linking tertiary institutions and Crown research institutes.
Chief executive Steve Cotter said the contract would be over 25 years and was contingent on the cable proceeding.
Hawaiki's cable would compete with the Southern Cross cable, which is half-owned by Telecom.
Cotter said he had no in-depth knowledge of how likely it was Hawaiki would secure the funding it required to build the US$300m cable, but he was encouraged by reports of its progress.
"I am quite optimistic we will get a second cable," he said.
Reannz's budget includes $15m that was contributed by the Government to encourage a new cable.
A new cable would create a "vital new global link for New Zealand internet users" while also benefiting its research and education communities, Cotter said.
Hawaiki chief executive Remi Galasso said the contract demonstrated the Government's commitment to provide New Zealanders with state-of-the-art infrastructure and "addressed longstanding market demand for a second international cable".
Galasso said six weeks ago that he believed Hawaiki was a "few weeks away" from securing the funding it needed to commit to construction.
Southern Cross Cable chief executive Anthony Briscoe has argued has argued that a competing cable could backfire by undermining the chances of Southern Cross being able to replace its "figure of eight" cable network before the end of its engineering life, which may come in 2030.