The Phillies failed to claim a postseason berth in two seasons under Kapler. Despite the acquisition of prized free agent Bryce Harper in the off-season, Philadelphia underachieved with an 81-81 record in 2019.
"Several years ago, I promised our loyal fans that I would do everything in my power to bring a world championship team to our city," Phillies owner John Middleton said in a statement. "I will never waver from that commitment. ... I have decided that some changes are necessary to achieve our ultimate objective. Consequently, we will replace our manager.
"I am indebted to Gabe for the steadfast effort, energy and enthusiasm that he brought to our club, and we are unquestionably a better team and organization as a result of his contributions."
Kapler joined Pete Mackanin and Ryne Sandberg as the third consecutive Phillies manager to be fired after no more than two full seasons leading the team. Middleton said general manager Matt Klentak will conduct the organization's search for a new skipper.
"I have tremendous respect for this organization, this franchise and this city," Kapler said in a statement. "We came into 2019 with very high hopes. We fell short of those, and that responsibility lies with me. The next Phillies manager will inherit a team of talented, dedicated and committed players.
"There has been nothing more fulfilling in my professional career than the opportunity to work with the players on this team."
The Phillies also announced that pitching coach Chris Young, head athletic trainer Scott Sheridan and assistant athletic trainer Chris Mudd won't return next season. Hitting coach Charlie Manuel will return to his role as a senior adviser.
Philadelphia is the eighth team seeking a new manager this off-season, joining the Los Angeles Angels, Chicago Cubs, San Francisco Giants, New York Mets, San Diego Padres, Pittsburgh Pirates and Kansas City Royals.