The American defeated countryman Kevin Kisner 4 & 3 in the final at Austin Country Club to claim his third win in his last five starts and dislodge Jon Rahm as World Number One.
He had to hold off a stirring fightback from Dustin Johnson in the semi-finals but victory rarely looked in doubt against Kisner as Scheffler banished the heartbreak of losing in the final at last year's event.
Corey Conners finished third with a 3 & 1 victory over Johnson in the third-place match.
Scheffler's ascent to the top of the world game comes just 42 days after he claimed his first US PGA Tour title, beating the previous record held by Tiger Woods by 210 days.
"I never really got that far in my dreams," said an emotional Scheffler. "I never made it that far. I just love playing golf and I love competing and I'm just happy to be out here.
"I don't feel like number one in the world. I feel like the same guy I was four months ago and I hope that doesn't change.
"Life is good. Life has been good to me for the past few years. I'm just really pleased with today's results and I just couldn't be happier.
"Getting denied here in the final last year was definitely tough and it would have stung even worse having to do that two years in a row.
"I got off to a good start this afternoon, made some nice putts and just kept my head down and kept playing some good golf."
A favourite among the local crowds due to his days at the University of Texas, Scheffler has proved himself to be an excellent match play operator, getting all the way to the final here last season and then winning 2½ points in the United States' record Ryder Cup victory.
I never really got that far in my dreams. I never made it that far. I just love playing golf
A tight win over defending champion Billy Horschel was followed by a victory over Seamus Power in the quarter-finals, before Johnson recovered from 5 Down to win four holes on the spin, eventually falling 3 & 1 in the semis.
Scheffler's reward for his run in Austin sees him go from zero to three US PGA Tour wins in six weeks and become the sixth youngest World Number One ever at the age of 25.
For 2019 champion Kisner, it is a second defeat in the final but his remarkable record at Austin Country Club since 2016 still reads 22 wins and just seven losses from 30 matches.
"I played solid every day," he said. "I couldn't get it going with the putter in the final match and Scottie is probably playing the best golf on the planet right now. I knew I needed my best and just couldn't hole anything to get any momentum my way.
"Hats off to him. He's playing great. Like I told him after: enjoy the hell out of how well you're playing, man."
Both men showed their intent as the first was halved in birdies but Kisner fell behind as he failed to get up and down from the sand at the second.
Scheffler holed a 20-footer on the fourth to move 2 Up and made a smart up-and-down to win the par-five sixth, with the next five holes halved in pars.
He looked in trouble when he hit a poor second at the par-five 12th and then duffed his chip into a bunker but he holed from the sand, forcing Kisner to make make a clutch putt to halve the hole in birdies.
A poor attempted bump-and-run from Kisner on the 14th led to a bogey and Scheffler was 4 Up with four to play, closing out victory with a half on the next.
In the third-place match, Johnson made a bogey-bogey start and Conners birdied the third and sixth, with Johnson birdieing the seventh to trail by three at the turn.
Johnson also won the 12th with a birdie but shook hands at the 17th as he found himself further away from the pin in two shots than Conners was in one.