The two-time major winner from Spain, who made the jump to the breakaway league last December, captured his second victory in the past three events, sandwiched around a runner-up finish to Brooks Koepka in a playoff at LIV Golf Greenbrier in August.
Rahm, who hasn't finished outside the top 10 in 11 events, arrived at Bolingbrook Golf Course near Chicago this week with Joaquin Niemann - a two-time winner this season - his only rival for the season title.
After a six-under-par second round on Saturday, Rahm took a one-shot lead over compatriot Sergio Garcia into the final round, with Niemann three adrift and needing to finish in front of Rahm to bag the individual champion's bonus.
Rahm had birdies at the third, sixth and 10th holes, and after letting a couple of birdie chances go begging, he sealed it with his birdie at 17, carding a four-under final round for a 54-hole total of 11-under par.
"I woke up really nervous today," Rahm said. "I wanted to do a really good show and get it over the line. Just really happy I played as good as I did.
"To go bogey-free on the weekend, one bogey all tournament, it's quite spectacular," he said. "I'm very proud of the putt on 17, which made 18 a lot, a lot, easier."
In addition to his $18 million champion's bonus he bagged $4 million for the tournament win.
He finished three shots better than Niemann, whose four-under final gave him an eight-under total that left him tied for second with Garcia.
The LIV season concludes next week with the team championship in Dallas.
After that, Rahm has his sights set on playing a trio of DP World Tour events to maintain his Ryder Cup eligibility.
He said Wednesday he was unwilling to pay the fines levied by the DP World Tour on golfers who fail to obtain releases to play in LIV events that conflict with tour tournaments.
Rahm has reportedly appealed the fines, and as that process plays out would be eligible to tee up at the Spanish Open later this month.
He also wants to play the Andalucia Masters and the Alfred Dunhill Links Championship.