More than 200 rooms and suites are set to be redesigned, while new features and facilities include the addition of river suites.
The resort will be closed while the works take place, and is due to reopen from 4 November in time for the winter season.
Sandals said the renovation formed part of its plans to celebrate the 25th anniversary of its operations in the Bahamas.
"Sandals Royal Bahamian has a storied past and played a starring role in the history of Bahamian tourism, hosting rock stars and royalty and we pledge our continued commitment to this captivating island," said Sandals Resorts International executive chair Adam Stewart.
