Pacific Fibre was set up in 2010 by local business and IT leaders to construct an undersea cable linking New Zealand with Australia and the United States to cater for increasing data use.
Pacific Fibre has secured about $US200 million worth of sales since its inception.
It doesn't name its fifth customer, an American firm, but says it is a signficant sale and it is winding up its fundraising drive.
Pacific Fibre has already signed up four firms including the Crown-owned research network REANNZ, Australian internet provider iiNet, and Vodafone.
Earlier this year, the Australian Financial Review questioned Pacific Fibre's ability to meet its $486 million fundraising target.