The combo dominated the opening day, setting the fastest time in nine of 10 stages to win Heat 1 by 28.4s over team-mates Lewis Bates and Anthony McLoughlin.
Molly Taylor and Malcolm Read ended the heat third before going fastest on the opening two stages of Heat 2 to take an early initiative.
A string of stage wins for Bates/McCarthy saw the Toyota Gazoo pairing reel in the Taylor/Read Subaru and take over the lead of the rally.
Holding a slender lead heading into the final stage, Bates/McCarthy then lost time to Taylor/Read, who fell just 0.2s short of the Heat 2 win.
For Bates and McCarthy it was enough to seal the Australian Rally Championship with a round to spare.
“I'm completely lost for words at the moment, I can't quite believe it,” Bates said.
“It was an incredible day and our team were here to see it and yeah it was all very special.”
Co-driver McCarthy added: “We should be pretty proud of ourselves. I think we've done a pretty good job managing everything this year
“Everyone speaks very highly of the talent we have have in Australia. We've got a good championship and it deserves to grow.”
Behind Taylor and Read in second in Heat 2 was Lewis Bates and McLoughlin in third.
The Australian Rally Championship finale takes place alongside Rally Australia, running from November 15-17 at Coffs Harbour.