Emergency services were called to a home on Weston Street, Revesby just before 8.50pm on Saturday where they located the pair, aged 36 and 48, inside a car.
NSW paramedics attempted to save the 48-year-old however she died at the scene.
The 36-year-old was taken to Liverpool Hospital in a critical condition, where she later died.
A man and a woman, who were unharmed, were also inside the vehicle at the time emergency services arrived.
Police said at least three burnt-out cars were located nearby at Moorebank, Lagoona and Revesby. It is not yet known if the cars are related to the shooting.
An investigation into the incident is underway and a crime scene has been established.
It is not known if the incident is linked to recent gangland shootings in Sydney.