The finding of a scientific team supports long-held suspicions the horse, affectionately known as Big Red, was fed arsenic about 35 hours before his death in 1932 as he began to make his mark on the US racing scene.
Seventy-four years later, using state of the art technology,
scientists have identified two forms of arsenic in six hairs and a sliver of hide taken from the champion New Zealand-born gelding.
One of the arsenic forms includes traces of lead consistent with substances used to preserve the horse's hide.
The other form was consistent with Phar Lap having ingested one single large dose of arsenic about 35 hours before his death, forensic hair analysis expert Ivan Kempson told reporters.
"All the material that we have can only indicate that he has
ingested arsenic, we can't actually identify where it's come from," Dr Kempson said.
The differences between the arsenic traces were distinguished using a synchrotron, the same technology used to identify the cause of Beethoven's death as lead poisoning.
"You will never get a 100 per cent definite answer that your confident there is no doubt about it," he said.
"But we can't explain it by any other way than the scenario of poisoning."
"A dose indicated to having been consumed so close to his death, well I think you can infer something from that," he said.
But while science may have answered the question of whether Phar Lap was poisoned, it has not found a way to determine who gave him the fatal dose.
The group is now comparing the results with samples of other preserved horses.
Phar Lap is Australia's best known race horse, winning 32 of his last 35 races.
His strapper, Tommy Woodcock, was always adamant the racer had been killed by US racing and gangster interests.