Joy Rainey, 61, from Evesham, Worcestershire, completed the challenge in Darwin at 12:30 Australian Central Standard Time.
Ms Rainey and her 110-year-old Oldsmobile covered more than 2,500 miles, taking 21 days.
She, along with 48 other drivers and their veteran cars, started from the Motor Museum of Australia in Adelaide.
The 1904 car has tiller steering, two gears and a top speed of 28mph (45km/h).
After crossing the finishing line, Ms Rainey said: "The Oldsmobile arrived in Darwin under her own steam, intact and sounding perfect as always.
"She is a fabulous 110-year-old horseless carriage and I am proud to be her owner."
Ms Rainey, who is of restricted growth, became the only woman to have driven across the US - from the west coast to the east coast - in a single-cylinder car.
The daughter of motor racing champion Murray Rainey, Ms Rainey has a background of karting and hill-climbing.
During the 1970s she held the ladies' outright record at many hill-climb venues in the UK.
A former racing car champion has become the first woman to cross central Australia in a single-cylinder vehicle.