The "Clueless" actress died suddenly in 2009 at just 32 years old. The autopsy blamed pneumonia and other factors.
After demanding more tests and suing the Los Angeles County Coroner's Office last year, Murphy's father submitted his daughter's hair, blood and tissues for independent lab testing.
"I have a feeling that there was a definite murder situation here," he told "Good Morning America." "It's poison, yes, I know that."
According to the results of the lab report, which was first reported by Examiner.com and obtained by ABC News, testing on the samples showed high levels of 10 heavy metals commonly found in rat poison.
"Brittany Murphy's death is highly suspicious," attorney Cyril Wect told "GMA." "It is a report from an accredited laboratory. It cannot be ignored."
The coroner's office says it stands by its original autopsy.
Just five months after Murphy's death, her husband Simon Monjack also died. His autopsy showed the causes to be pneumonia and anemia.
ABC News contributed to this report.