The decision has come around a month earlier than anticipated with BHP indicating in its quarterly it expected to take FID in the latter half of the September quarter.
Ruby has estimated recoverable 2C resources of 13.2 million barrels of oil and 274 billion cubic feet of gas.
The project will include a shallow water tie-back from wellhead protector platform to two existing BHP offshore platforms.
First production is expected in 2021 and according to BHP, will increase production from its Trinidad and Tobago assets by 16,000 barrels of oil per day and 80 million cubic feet per day at its peak.
Total investment in the field is expected to reach US$500 million (A$740 million). BHP as operator will front up US$283 million.
"This is an important milestone for BHP in Trinidad and Tobago. Ruby aligns well with our strategy of maximising value from our existing assets, brining competitive near term value and volume growth," BHP president operations petroleum Geraldine Slattery said.
Gas from the project is expected destined for the Trinidad and Tobago market.
The board's approval of the Ruby project follows a successful drilling campaign in Trinidad and Tobago, with BHP drilling the Bele-1, Tuk-1 and Hi-Hat-1 exploration wells over the last quarter.
So far this year seven out of the nine wells the company has drilled were successful.
BHP was first awarded the Block 3(a) by the Trinidad and Tobago Ministry of Energy and Energy Industries in October 2001.
The Block is comprised of around 150,000 acres and is located 25 miles off the northeastern coast of Trinidad in 300 feet water depths.
BHP holds a 68.46% stake in the Ruby Project alongside Heritage Petroleum and the National Gas Company of Trinidad and Tobago holding the remaining 20.13% interest and 11.41% interest respectively.
BHP was up 0.5% at $36.97 per share.