The news was first reported Wednesday night by Golf.com.
Mickelson, who began working with Harmon shortly before the 2007 Players, won 12 PGA Tour events and three international tournaments during that span, including the 2010 Masters and 2013 Open Championship.
That victory at Muirfield represents Mickelson’s most recent title. Since then, Lefty has posted just five top-10 finishes while slipping to No. 25 in the world. To play in last month’s Presidents Cup, his 21st consecutive team competition, he required a captain’s pick.
In a statement released to Golf.