The hotel, in San Juan, will add 3,250sqm of meeting space to the 54,000sqm already available at the neighbouring convention centre.
The 503-room property, built in partnership with Caribbean developer Interlink Group, will also offer dedicated outdoor event space on its 5,300sqm pool deck, a ballroom, spa, casino, fitness centre and shops.
It has been built as part of Starwood's multi-billion pound global effort to revitalise its Sheraton brand.
In addition, Starwood will double its presence in Puerto Rico next year with the launch of the W Retreat and Spa on Vieques Island and the St Regis Resort and Residences Bahia Beach.
Starwood senior vice-president of development for North America Paul Sacco said: "The temperate climate, strong infrastructure and proximity to gateway cities in the US, Mexico and South America make Puerto Rico an extremely attractive growth market for Starwood."