The former world No.2 and British Open winner was the only man to miss all four cuts in the majors last season and has failed to reach the weekend in his past six, including last month's Masters.
Coach Grant Field has been in Smith's corner since he was a Brisbane junior but, after a rough second round at Augusta National led to his latest premature exit, a tough call was made.
Claude Harmon III, the son of swing guru Butch Harmon, is working with Smith this week at Aronimink Golf Club in Pennsylvania ahead of the PGA Championship.
"It was a terrible, terrible conversation to have," Smith told todaysgolfer.com of the decision to split with Field.
"I've been seeing Grant since I was like nine years old, and he's a really good friend as well, so it was tough.
"But I feel like I have done the right thing for my golf. I think what I've done is right.
"I just need to go out there and do it ... and get some confidence back."
A perennial contender at Augusta, Smith was gutted to miss the weekend's action for a second-straight year.
"It's been a rough time in the majors for sure," the LIV Golf product said at the time.
"I'd like to think probably early in my career that I hung my hat on how I performed in the majors and it's just not good enough.
"Making a few changes to try and get back to where I was, and better. I can promise you the fire is in the belly. It's just a matter of time."
The coaching change comes after the 32-year-old smiled away questions about retirement, given the uncertainty surrounding LIV Golf's future.
But Aronimink, hosting the PGA for the first time since 1962, could bring out the best of a golfer like Smith who relishes craft and creativity over brute force.
Harmon, whose father mentored Tiger Woods for eight of his 15 majors, coaches fellow LIV talent Dustin Johnson.
"It's just a bit of a different outlook," Smith said.
"It's not rocket science. I got to a point where I was thinking so many things in my golf swing that I couldn't hit the golf shot, which is never a fun place to be.
"He just really simplified it and made me think one thing rather than a thousand.
"It's starting to feel good and starting to feel like I can actually commit to some shots and hit some different shots, so it's coming along nicely.
"Claude spends a lot of time out on LIV with DJ. He's obviously got a wonderful reputation."
Previous winner Jason Day, Adam Scott, Min Woo Lee, Elvis Smylie and Travis Smyth are the other Australians in the field when round one begins early on Friday morning (AEST).
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