The American shot a five-under-par 67 on Sunday to finish on nine-under-par, leaving him with an insurmountable 42-point lead over Branden Grace of South Africa.
Johnson finished in the top five in four of the previous five events, taking home $4 million for his only win of the series in Boston in September.
"Locking up the individual competition is big. It's an honour to be LIV's first individual season champion," Johnson said.
Patrick Reed, the 2018 Masters winner, sits in third in the overall standings while British Open champion Cameron Smith is in fourth spot. The runner-up will be awarded $8 million while the third-placed player earns $4 million.
The individual competition concludes in Jeddah from October 14-16 before a final team championship at former US president Donald Trump's Doral course in Miami.
"The first chapter of LIV Golf's history could not be written without Dustin Johnson's name," LIV chief executive Greg Norman said.
"By any measure, DJ is among the elite players in the world. From the start, he's been an LIV Golf cornerstone. He has more than lived up to his billing and deserves immense credit."
LIV Golf has lured away some of the US-based PGA Tour's top members with huge sums of money, leading to a simmering feud between the sport's top players and organisers.
LIV tournaments do not count towards the world rankings, and players who compete in the breakaway series have been suspended from the PGA Tour.
The series is s bankrolled by the Saudi Arabia Public Investment Fund and critics have accused it of being a vehicle for the country to attempt to improve its reputation in the face of criticism of its human rights record.
