Scheffler is the first player since Arnold Palmer in 1962 to pile up six wins before July 1 on the PGA Tour, a haul that included his second Masters crown in April.
"It's pretty special," Scheffler said. "It's been a great season. I've been fortunate to come away with some wins and it's been a lot of fun.
"Tom played his heart out today," Scheffler added. "It was fun battling with him."
He grabbed the win with a bogey-free five-under par 65 for 22-under 258, maintaining his composure after Kim birdied the 72nd hole to force the playoff shrugging off a spell of confusion as a handful of climate protesters ran onto the 18th green with cannisters spraying colored smoke.
"Fortunately for Tom and me, we're great friends so we were able to kind of sit there and really relax each other," Scheffler said of the "confusing" protest.
"You don't really understand the situation. There's people running around everywhere and you don't really know what's going to happen. Fortunately the police did a great job getting everything in order very quickly."
Kim, who started the day at TPC River Highlands in Cromwell, Connecticut, with a one-shot lead, fired a final round 66.
But it was a shootout on the rain-softened course, with half a dozen players holding a piece of the lead and five sharing the top spot for much of the afternoon.
Scheffler and Kim were at the top through 13 holes.
Scheffler inched in front with a second straight birdie at 14, where his approach from the fairway left him three feet for birdie. Kim bombed a massive drive but his wedge to the green left him 16 feet and he settled for a par.
After Scheffler left his 14-foot birdie putt at the par-three 16th inches short, Kim missed a golden opportunity to pull level when he left his own 10-foot birdie try short.
Both parred 17, where Scheffler's 16-foot birdie putt settled on the lip of the cup.
After Scheffler's approach at 18 got hung up in the fringe, Kim fired at the flag, his ball bouncing within inches of the cup before leaving him a 10-foot birdie putt.
As the players were sizing up their putts the protesters, some of them wearing T-shirts reading "No golf on a dead planet" raced onto the green. They were quickly tackled by police and security staff and marched away.
Scheffler stepped up to putt first and after he settled for a par Kim rattled in his birdie putt to tie it up.
They returned to 18 for the playoff. Both were in the fairway, but Scheffler's second shot threatened the pin to leave him an 11-foot birdie chance.
Kim's approach was plugged in a greenside bunker, his shot out leaving him 36 feet for par. He missed, and Scheffler two-putted for the win.
As the last group drama played out, Tom Hoge was already in the clubhouse on 20-under after a career-low round of eight-under par 62 that featured nine birdies.
Tied for the lead as he walked off the course, Hoge finished tied for second with South Korean Im Sung-jae, who was four-under over his last six holes to card a 66.
Patrick Cantlay, Tony Finau, Justin Thomas and Akshay Bhatia shared fifth on 262.
