"Cathriona White, 30, was pronounced dead by paramedics Monday evening," Fred Corral, a spokesman at the Los Angeles County coroner's office, told AFP.
He said Ms White's death was being treated as a suicide. Local news reports said the couple, who have been dating on-and-off since 2012, broke up last Thursday.
Ms White sent a cryptic message on her Twitter account that day that read:
Signing off Twitter, I hope I have been a light to my nearest and dearest. to yo all? Cathriona white (@littleirishcat) September 24, 2015
Jim Carrey said in a statement that he was "deeply saddened by the passing of my sweet Cathriona." (Also Read: Jim Carrey Not Interested in Getting Hitched Again?)
"She was a truly kind and delicate Irish flower, too sensitive for this soil, to whom loving and being loved was all that sparkled," the 53-year-old actor added.
"My heart goes out to her family and friends and to everyone who loved and cared about her. We have all been hit with a lightning bolt," he said.
Ms White was found at her home on the evening of September 29 by a friend who called emergency services. She had reportedly left behind a note.