Ogier's calmness shone through after heavy rain transformed the gravel forest roads into a muddy mess.
He was faultless while both Neuville and overnight leader Tanak escaped brushes with the scenery during the morning's opening three speed tests.
Ogier could afford a celebratory drive through the final Power Stage in the knowledge the championship was already secured in his final appearance in M-Sport's Ford Fiesta before switching to Citroen in 2019.
A composed drive to fifth at Kennards Hire Rally Australia was in marked contrast to the heartbreak suffered by Neuville and Tanak, who both crashed whilst trying to keep their hopes alive.
"It's been an incredible season, so close. Not so long ago we were thinking it was going to be tough to grab this title but we never gave up," said Ogier.
We gave everything, with a fantastic team behind us who kept fighting and in the end we grabbed it in the last rally. It's so emotional," the Frenchman added.
Ingrassia shared Ogier's views.
"We had a beautiful journey with M-Sport over these two years, and everything we achieved we achieved together. We wanted to end our time with Malcolm and the team in a special way, and that is what we did.
There have been a lot of ups and downs during the season and the rally, and we gave it everything to achieve this amazing result!"