Former Hawaii resident Q'orianka Kilcher, who played Pocahontas in Terence Malick's 2005 epic "The New World" opposite Colin Farrell, will star.
Forby will be joined by producers Nigel Thomas and Lauri Apelian of Matador Pictures, the team behind British director Ken Loach's Irish civil war film "The Wind That Shakes the Barley." That film took the Palme d'Or award at last year's Cannes Film Festival.
The Hawaii film, being made with a $9 million (euro6.7 million) budget, will mark Forby's directorial debut.
Forby, who also wrote the script, plans to tell the story from Kaiulani's perspective.
"It's as much about the growth of a young woman into a stateswoman as it is about the demise of a nation. She's the cinematic way to tell that story," he said.
Kaiulani, who was of Hawaiian and Scottish descent, was 17 when U.S.-backed businessmen overthrew the Hawaiian monarchy. The princess sailed to Washington, D.C., from England, where she was studying, to lobby President Grover Cleveland and the U.S. Congress to put Hawaii back under monarch rule. Cleveland was sympathetic, but Congress stood by the provisional government in Honolulu. Hawaii was made a republic in 1898.
Years later, Kaiulani caught a severe cold after getting caught in a tropical rainstorm on the Big Island. The cold lingered for months before killing her in March 1899.
Forby's past credits include producer for "29 Palms," a movie about an undercover FBI agent who uncovers illegal gambling activities at an Indian casino.