Cathriona White, 30, who was from County Tipperary in Ireland, was found dead on Monday of a suspected overdose.
Police told the Associated Press the matter was being treated as a suicide but no conclusion has yet been reached.
The website TMZ.com said the couple had an on-off relationship and broke up again last week.
"She was a truly kind and delicate Irish flower, too sensitive for this soil, to whom loving and being loved was all that sparkled," Carrey said in a statement.
The Canadian actor, 53, who starred in Dumb and Dumber and Ace Ventura Pet Detective, met White, a beauty therapist, in 2012.
The Irish Times said White moved to California in 2009 and became involved with Carrey after meeting him on a film set.
Her last tweet, written on Friday, said she was "signing off" from Twitter, adding: "I hope I have been a light to my nearest and dearest."
Hollywood actor Jim Carrey says he is "shocked and deeply saddened" by the death of his former partner in her Los Angeles apartment.