The man, named as Stephen Buscumb, was struck by the motorcycle while cycling at about 7.30am on Thursday.
Buscumb died from head and neck injuries despite wearing a cycling helmet, police said.
According to the police reports Buscumb was in the left lane when he fell into the path of an oncoming motorcycle.
The rider, 28-year-old factory worker Mongkholruek Klansaisook, said the accident occurred just as he was preparing to overtake the Australian.
Thai media reports say the two vehicles may have come into contact before Buscumb spilled from his bike.
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The motorbike rider tried to assist the Australian, but Buscumb died before emergency medical aid could reach the scene.
Deputy police investigator Pitthaya Sriruang, said a full investigation would be carried out into whether the motorcyclist should face charges of reckless driving.
The Australian had lived in Thailand for about 10 years, and worked as a chemical engineer.
