The 53-year-old was in a coma after her car burst into flames when it crashed into a house on August 5.
Her family issued a statement yesterday saying she was not expected to survive.
"We want to thank everyone for their kind wishes and prayers for Anne's recovery and thank the dedicated staff and wonderful nurses," it said.
As well as suffering burns, Heche was left with "a severe anoxic brain injury" - when the brain is deprived of oxygen - her family said.
A representative said the actress is "legally dead," but added that her life-support treatment would continue temporarily to check if she may be a match for a potential organ donation, the BBC reported.
No one inside the house was hurt in the crash, but the impact set the dwelling ablaze, requiring a response by dozens of firefighters.
According to a spokesperson from the Los Angeles Police Department, Heche had drugs in her system at the time of the crash.
Heche came to prominence for her Emmy-winning work on the daytime television drama Another World and went on to star in other screen roles including the HBO series Hung and such films as Wag the Dog and Cedar Rapids.
She made tabloid headlines in the late 1990s for an affair with comedian Ellen DeGeneres around the time that DeGeneres came out publicly as a lesbian.
Following their split, Heche wed cameraman Coleman Laffoon, but they later divorced, and she spent some years after that in a relationship with actor James Tupper, her co-star in the short-lived TV show Men in Trees.
- Reuters, BBC and NZ Herald
