The 29-year-old American had 13 birdies against a lone bogey to finish on 23-under 187 for the 54-hole event at the resort in White Sulfur Springs, West Virginia.
That was enough for a six-stroke victory over Chile's Mito Pereira, who fired a closing 63.
DeChambeau's score at the Old White course on the upstart Saudi-backed circuit matched the lowest round in US PGA Tour history, the 12-under 58 fired by American Jim Furyk in 2016 at TPC River Highlands in Cromwell, Connecticut.
The Old White hosted a PGA event from 2010 to 2019 and Australian Stuart Appleby fired a 59 in the final round of the inaugural event to win the title.
DeChambeau birdied 22 of his last 34 holes on The Old White for his first victory since the 2021 PGA Arnold Palmer Invitational at Bay Hill.
DeChambeau opened with back-to-back birdies, reeled off four in a row starting at the fourth hole, took his lone bogey at the par-3 eighth but followed with back-to-back birdies at nine and 10.
He birdied the par-5 12th then closed with consecutive birdies at the par-3 15th, par-4 16th and par-5 17th, knocking in a six-foot putt, and the par-3 18th, where he sank a long putt from over a ridge in rainy conditions then jumped for joy and pumped his right fist in celebration.
DeChambeau opened Friday with a 68 and matched the prior all-time low round in LIV's two-season history with a 61 on Saturday to pull within a stroke of 36-hole US co-leaders Matthew Wolff and David Puig.
