The 15-turbine project would be in federal waters 48km east of Montauk, Long Island and near New York City and New Jersey.
"This is a big day for clean energy in New York and our nation," said Deepwater Wind CEO Jeffrey Grybowski.
Deepwater developed the 30MW Block Island project off Rhode Island, which came online in December. It is the Americas' first offshore wind project.
A few days before the board's vote, LIPA and utility PSEG of New Jersey completed negotiations with Deepwater for South Fork. The site is expected to be online by 2022.
It is the first phase of Deepwater's 1GW Deepwater One project, for which the developer has a lease from the federal government.
New York State plans to reach 50% renewable energy by 2030, under plans unveiled by governor Andrew Cuomo.