Viktor Bout , the Russian arms dealer known as the “Merchant of Death,” walked out of a U.S. jail almost two years ago in a trade with Moscow for U.S. basketball star Brittney Griner . Now he is back in business, trying to broker the sale of small arms to Yemen’s Iran-backed Houthi militants .

The 57-year-old, whose life reportedly inspired the 2005 Hollywood movie, “Lord of War,” starring Nicolas Cage, spent decades selling Soviet-made weapons in Africa, South America and the Middle East before being arrested in 2008 in a U.S. law-enforcement sting operation.

Since his release, Bout has joined a pro-Kremlin far-right party and won a seat in a local assembly in 2023, seemingly turning the page on his days as an arms broker. But when Houthi emissaries went to Moscow in August to negotiate the purchase of $10 million worth of automatic weapons, they encountered a familiar face: the mustachioed Bout, according to a European security official and other people familiar with the matter.

The potential arms transfers, which have yet to be delivered, stop well short of the sale of Russian antiship or antiair missiles that could pose a significant threat to the U.S. military’s efforts to protect international shipping from the Houthis’ attacks.

The Biden administration has been worried that Russia might provide the Houthis with such advanced weapons to retaliate for Washington’s support of Ukraine, but there is no evidence that those missiles have been sent, or that Bout is involved in such a deal.

Still, even small arms shipments to the Houthis would be opposed by Washington, which has designated the Yemen militants as a terrorist group .

Arming a belligerent in the Middle East conflict would also mark an escalation for Russia, which has been strengthening security ties with Tehran but has generally stayed away from the confrontation between Israel and its Iran-backed foes.

Steve Zissou , a New York attorney who represented Bout in the U.S., declined to discuss whether his client had met with the Houthis.

“Viktor Bout has not been in the transportation business for over twenty years,” Zissou said. “But if the Russian government authorized him to facilitate the transfer of arms to one of America’s adversaries, it would be no different than the U.S. government sending arms and weapons of mass destruction to one of Russia’s adversaries as it has sent to Ukraine.”

The small arms deal that Bout was said to have been brokering was with two Houthi representatives who had traveled to Moscow under the cover of buying pesticides and vehicles and visited a Lada factory, according to the people familiar with the matter.

The people familiar with the deal didn’t know if the deal was being negotiated at the Kremlin’s behest or merely with its tacit approval. While the Houthis have been seeking Russian-made weapons, The Wall Street Journal couldn’t determine the specific source of the planned supply.

A Houthi spokesman declined to comment. The Kremlin didn’t return a request for comment.

The first two deliveries will be mostly AK-74s, an upgraded version of the AK-47 assault rifle. But during the trip, Houthi representatives also discussed other weapons the Russian side might potentially sell, including Kornet antitank missiles and antiaircraft weapons, according to the European official and other people familiar with the matter.

The deliveries could start as early as October to the port of Hodeidah under the cover of food supplies, where Russia has already carried out several grain deliveries, they said.

When Bout was released in the December 2022 prisoner swap , White House officials described it as a difficult decision but the only way to get Griner out of a Russian penal colony. They emphasized that Bout had already served 12 years in U.S. prisons.

National-security adviser Jake Sullivan said at the time that the U.S. government had done an assessment of the risks of Bout’s release before the exchange and had concluded they were acceptable.

“We believe we can manage those challenges, but we will remain constantly vigilant against any threat that Viktor Bout may pose to Americans, to the United States going forward,” Sullivan said. “I would just point out that there is no shortage of arms traffickers and mercenaries in Russia.”

A spokesman for the National Security Council didn’t respond to a request for comment on Bout’s current activities.

Since his release from prison, Bout has often appeared on Russian television as a commentator on Russian politics and a critic of the U.S., which he has said is determined to dismantle Russia. He has also been cited occasionally in the Russian media as an expert in the weapons trade.

He said that he kept a portrait of Russian President Vladimir Putin on the wall of his cell throughout his confinement in the U.S., and has strongly supported the invasion of Ukraine.

Sales to the Houthis would extend Bout’s decadeslong career in selling arms to some of the world’s most controversial customers. Born in 1967, in Dushanbe, Tajikistan, then part of the Soviet Union, according to official records, Bout served as a military translator, learning French, English, Arabic, Farsi and Portuguese. He was sent to assist Angolan forces during a 1980s civil war.

After the Communist bloc dissolved in 1991, he purchased Russian military cargo planes and used them to transport United Nations peacekeepers in Africa. Bout first came in the public eye after the U.S. in 2005 sanctioned him for trading weapons for diamonds with Charles Taylor , a former Liberian president and convicted war criminal. U.N. experts also accused him of violating international arms embargoes on Angola and the Democratic Republic of the Congo.

Arrested in Thailand in a 2008 sting operation led by U.S. Drug Enforcement Administration agents posing as Colombian leftist rebels, he was convicted in 2011 of conspiring to kill Americans and attempting to sell weapons to Colombian rebels. He was sentenced to 25 years in prison.

The Houthis have repeatedly attacked international shipping and have launched drone and missile attacks against Israel. The U.S. and Israel have carried out airstrikes in response, including on Friday when the American military struck 15 Houthi targets.

Write to Benoit Faucon at benoit.faucon@wsj.com , Michael R. Gordon at michael.gordon@wsj.com , Warren P. Strobel at Warren.Strobel@wsj.com and Alan Cullison at alan.cullison@wsj.com