The announcement came with the unsurprising news of a fourth-season pickup for the series. It continues AMC's rocky record with its showrunners, but the network said the decision was mutual.
While AMC has clashed with showrunners before over money, a person familiar with the situation told TheWrap that this time the issue is "100 percent not about money or contracts."
Rather, it is about a difference of opinion over where the show should go in the fourth season and beyond. It involves AMC, Mazzara and the show's writers and producers, who include Robert Kirkman, creator of the comics that provide the basis of the series.
Kirkman might be the fans' choice to take over as showrunner, given that most of its characters were born on his pages. But he also has a busy career writing comics and novels.
In a statement, Kirkman said he believes Mazzara and AMC came to the decision "in the best interest of the future of the show."
In an interview with TheWrap in October, Mazzara said he would love to remain with the show until the end, "if AMC and the fans would have me."
"I would love to be the guy shutting the lights off," he said at the time.
It didn't work out that way, even though Mazzara has made "The Walking Dead" this season's top-rated drama — even beating network shows. It also has a legimimate shot at ending the season as TV's top scripted show overall.
"Both parties acknowledge that there is a difference of opinion about where the show should go moving forward, and conclude that it is best to part ways," AMC said in a statement.
AMC also said the decision is "amicable" and that Mazzara will remain showrunner for the remainder of the third season, which resumes airing in February. The episodes have already been filmed, and Mazzara will oversee postproduction.
He is also looking for his next project.
"My time as showrunner on 'The Walking Dead' has been an amazing experience, but after I finish season 3, it’s time to move on," said Mazzara. "I have told the stories I wanted to tell and connected with our fans on a level that I never imagined. It doesn’t get much better than that. Thank you to everyone who has been a part of this journey."
Mazzara took over the show after Darabont parted ways with it after its first season. Darabont was just one of several showrunners to have issues with AMC.
Jason Horwitch left "Rubicon" during its lone season. The third season of "Hell on Wheels" was briefly put on hold last month when showrunner John Shiban left. "Mad Men" creator Matthew Weiner nearly walked from the show during a contract dispute last year. And "Breaking Bad" briefly looked into leaving AMC before creator Vince Gilligan's contract was renewed.
Kirkman's full statement included his thanks to Mazzara and the show's fans.
"I am in full support of both AMC and Glen Mazzara in the decision they have come to and believe the parties came to this decision in the best interest of the future of the show," Kirkman said. "I thank Glen for his hard work and appreciate his many contributions to 'The Walking Dead' and look forward to working with him as we complete post production on Season 3. I am also excited to begin work on another spectacular season of this show that I know means so much to so many people. This show has always been the result of a wide range of extremely talented men and women working tirelessly to produce their best work collectively. I believe the future is bright for 'The Walking Dead.' Thank you to the fans for your continued support."
Executive producer Gale Anne Hurd also expressed her thanks.
"I am appreciative and grateful to Glen for his hard work on ‘The Walking Dead,’" she wrote. "I am supportive of AMC and Glen's decision and know that the series is in great hands with one of the most talented and dedicated casts and crews in the business. I look forward to the show's continued success.”