He won a big Netflix deal. Then Saudi Arabia convicted him as a terrorist.

Saudi Arabia has now also convicted him as a terrorist.

Almuzaini, who was born in Texas and holds U.S. citizenship, revealed last week that a secretive Saudi court originally set up to try al Qaeda militants has sentenced him to 13 years in prison and a 30-year travel ban over tweets posted more than a decade ago.

Some of the tweets referenced in court documents viewed by The Wall Street Journal ridiculed Arab regimes—“Nobody can save Palestine but God. Arab countries can barely save themselves," Almuzaini posted in 2015—or voiced support for women’s rights. In 2014, before recent social reforms, he wrote, “You cannot live in Riyadh unless you get high."

That irreverence earned his Myrkott Animation Studio a five-year partnership with Netflix in 2020 that made Saudi content available to global audiences—one of the first deals of its kind for any studio in the Middle East. The streaming platform has carried two seasons of his “Masameer County" and a feature-length film.

To the Saudi judiciary, his saucy tweets amounted to a crime. Prosecutors charged him with attempting to destabilize society and sending content over the internet that could harm public order, the documents show.

“It has been established that the defendant is guilty of endorsing extremist ideas and attempting to destabilize the social fabric and national unity," the court said in its initial ruling in July 2023, according to the documents. The decision was upheld on appeal in April. A final appeal is pending.

Almuzaini denied the charges and said the tweets were sarcastic or in line with current Saudi policies, according to the documents.

His predicament reflects the duality of life in the kingdom in the midst of a reform drive spearheaded by Crown Prince Mohammed bin Salman. While Saudi Arabia has eased social prohibitions against driving by women, gender mixing and public entertainment, it remains an autocracy where security agencies operate with few checks on their power.

The Specialized Criminal Court that convicted Almuzaini has since 2017 sentenced scores of government critics including high-profile women’s rights activists, liberal writers and even Islamist clerics. Some nonviolent offenders convicted of tweeting criticism of Saudi rulers or support for political prisoners have received staggering prison sentences.

Abdulrahman al-Sadhan, a U.S.-educated aid worker, was sentenced in 2021 to 20 years in prison. The only pieces of evidence presented in his closed-door trial, he told his sister, were tweets critical of the government that he allegedly published from an account satirizing Islamist extremists. A Saudi official has said Sadhan confessed to supporting terrorism.

Since 2022, social-media posts have brought two ordinary Saudi women prison sentences of 35 years and 45 years, and got a retired teacher sentenced to death.

Saudi officials didn’t respond to a request for comment about Almuzaini’s case. Asked about severe punishments meted out for critical tweets, the crown prince said that his government was “doing our best" to change the situation and acknowledged that it would take time to fix.

“We are not happy with that. We are ashamed of that. But the judicial system have to follow the laws and I cannot tell the judge, ‘Do that and ignore the law,’ because that’s against the rule of law," he told Fox News in September. “But do we have bad laws? Yes. Are we changing that? Yes."

In an interview from Riyadh, Almuzaini said he believes his case was the result of an oversight that he wants to see cleared up so he can continue living and working in the kingdom.

“I’m pro-Saudi," he said. “I love my country. I wish for more openness. I think we should do more."

Adding to the unusual nature of the case: Almuzaini still lives freely at home in Riyadh despite the conviction. Saudi authorities never asked Netflix to remove any of the content in question, though it has prompted Netflix to take down other material at least once in the past.

The State Department is monitoring Almuzaini’s case and seeks to ensure a fair and transparent legal process, a spokeswoman said. Netflix declined to comment.

Almuzaini said that his case was the result of individuals’ mistakes and that he hopes it serves as an alert for Saudi authorities.

“Despite the government’s efforts to reform the kingdom as fast and as big as possible, there are individuals who may cause collateral damage to these efforts," he said.

In a video he posted online, Almuzaini accused a midlevel functionary at the state media regulator of misconstruing comedic scenes from his popular Netflix show to build a national-security complaint of endorsing terrorism and homosexuality, which is criminalized by Saudi law. The employee badgered him to work with a Saudi-owned broadcaster rather than Netflix, he said.

International criticism of Saudi Arabia’s crackdown on its critics, which was galvanized by the 2018 killing of the Saudi journalist Jamal Khashoggi, largely subsided after President Biden met with Prince Mohammed in 2022, reversing a campaign promise to treat the kingdom like a pariah over its human-rights record. Riyadh has since repaired relations with Washington, redoubled its efforts to attract foreign tourists and investment and positioned itself as a serious player in global affairs from Gaza to Ukraine.

What makes Almuzaini’s case stand out is that it was unfolding in secret proceedings even as he was producing shows for Netflix, collaborating on state-run entertainment initiatives and being featured at ministerial-level events and on government television.

His commercial success has been a boon for Saudi Arabia’s nascent efforts to develop a film industry with foreign capital and expertise, part of its broader efforts to diversify the economy away from oil.

“If even being sort of a fellow traveler with the direction the state wants to go isn’t enough to secure your position, then it definitely raises some questions about the risks that creatives are taking within the kingdom," said Kristin Smith Diwan, a senior resident scholar at the Arab Gulf States Institute in Washington who writes about cultural shifts in the region.

Some Saudi rights activists said it is unlikely Prince Mohammed or officials close to him wouldn’t have been aware of such a high-profile case.

“These kind of things are top level. MBS is very, very centralized," said Abdullah Alaoudh, senior director for countering authoritarianism at the Middle East Democracy Center, a U.S.-based advocacy nonprofit, referring to the crown prince. Alaoudh’s father, a popular cleric, has been on trial for more than six years at the same terrorism court that sentenced Almuzaini.

“It’s impossible for years this fiasco is going on and nobody knew," he said.

Almuzaini, 42, co-created the “Masameer" franchise in 2010, publishing animated videos on YouTube that satirized religious hard-liners and advocated liberal reforms years before the crown prince came to power. He later set up Myrkott and produced a feature-length “Masameer" film that was shown in theaters in 2020 after the kingdom ended a 35-year ban on cinemas. A sequel is due out on Netflix this month.

One of the main “Masameer" characters is Bandar, a Saudi man whose wealthy upbringing shelters him from the ways of the world and gets him into trouble. He is a regular target of the show’s parody.

In his video last week, Almuzaini said the government employee cited alleged violations of the kingdom’s media guidelines, including a scene from his animated show “Masameer County" on Netflix depicting the former Islamic State leader Abu Bakr al-Baghdadi.

In the episode, Bandar goes looking for ice cream and eventually ends up lost in a desert where he runs into a bearded Islamic State recruiter. “What if I told you about a wonderful place where you could eat all the ice cream that you would ever want and you don’t ever have to stop, even if you’re full?" the recruiter asks. “Chocolate, vanilla, strawberry, whatever you want."

Bandar travels to the caliphate, encounters Baghdadi and is knocked unconscious. In a dream sequence, he climbs a celestial staircase and finally gets his ice cream.

Almuzaini said the government employee told him the episode, intended as mockery, promoted joining jihadist groups.

“He’s the only one who reads it that way. I didn’t write it that way at all. Of course the matter is very strange," Almuzaini said in the online video. “We as Myrkott and I as the chief executive are not ISIS nor are we terrorists."

His terrorism conviction and the lack of transparency surrounding it have put his promising production career at risk. Myrkott’s Saudi operating license was revoked when the case began, forcing it to close, dismiss all its employees and forgo lucrative expansion and acquisition opportunities.

“I was forced to close," Almuzaini said. “Myrkott has stopped after all these years, after all this work and exertion."

Write to Stephen Kalin at stephen.kalin@wsj.com and Jessica Toonkel at jessica.toonkel@wsj.com