Parler, a moderation-light social-media network that was forced offline last month by tech giants over how it policed its content, has fired its chief executive amid a dispute over the platform’s future.

John Matze, the former CEO, said he was fired on Friday by the company’s board as the platform was within days of restoring service to its roughly 15 million users. He said the board is currently controlled by conservative political donor Rebekah Mercer.

“Over the past few months, I’ve met constant resistance to my product vision, my strong belief in free speech, and my view of how the Parler site should be managed,” he said in a statement. “For example, I advocated for more product stability and what I believe is a more effective approach to content moderation.”

Dan Bongino, a conservative talk-show host who has invested in Parler, responded with a Facebook video saying that Mr. Matze bore responsibility for “really bad decisions” that led to Parler being taken offline as well as problems with the app’s stability.

“John decided to make this public, not us, “ Mr. Bongino said. “We were handling it like gentlemen.”

The immediate impact on Parler’s efforts to restore service to its roughly 15 million users isn’t clear, though a person familiar with the company said that Mr. Matze had created Parler’s original code. Mr. Matze told the Journal that the site had overcome most of the hurdles to restoring service both through its website and for people who had previously downloaded its app.

“Anybody who still had the app could have gotten on it” when service is restored, he said. “But no new accounts.”

Mr. Matze said that before he was fired he had been seeking to adjust the platform’s moderation rules in ways that would allow Parler to return to Google’s and Apple Inc.’s app stores.

Representatives for Parler and Ms. Mercer couldn’t be reached for comment on Mr. Matze’s firing or the timing of Parler’s relaunch.

In the months following the U.S. presidential election, Parler carved out a niche but rapidly growing place in social media by wooing conservatives disaffected by mainstream platforms’ efforts to label certain speech and ban users who they deemed to have violated their guidelines around hate speech, misinformation and false claims of victory by former President Donald Trump.

Parler’s rules forbid criminal activity and threats, but the platform left moderation up to community “jurors,” users who addressed content violations and were paid part-time.