As an arms trafficker, he operated in some of the world’s most dangerous places, becoming one of the world’s most wanted men and earning the nickname “Merchant of Death,” not to speak of a 25-year prison sentence in the U.S. But now, nine months after returning to Russia in a prisoner exchange, Viktor A. Bout is reinventing himself — as a local politician.

Mr. Bout, 56, is standing in elections Sunday as a candidate for the regional assembly in Ulyanovsk, a territory of 1.3 million people about 450 miles east of Moscow that was Lenin’s birthplace. His emergence as a politician in Russia’s autocratic system — in which elections serve mainly to add a veneer of legitimacy to President Vladimir V. Putin’s rule — shows how the Kremlin is eager for fresh faces to maintain popular support.

“I’ve been for 15 years locked up in your federal system,” he said in an interview conducted in somewhat stilted English at his party’s Moscow headquarters. “So what do you expect for me, that I have to take time to take vacation? Heck no. I’ve got to do everything for my country.”

Mr. Bout (pronounced “boot”) was arrested in Thailand in 2008 in a U.S. sting operation, convicted in 2011 in a Manhattan court and sentenced to 25 years in prison on four felony charges, including conspiring to kill Americans and conspiring to provide material support to a terrorist organization. He had built his empire during the wild, post-Soviet era of wanton crime and corruption, sending a fleet of airplanes around the world to deliver arms to rebels, terrorists and militants, analysts and American intelligence agents have said. He was long suspected of having links to Russia’s military intelligence agency, the G.R.U.

He returned to Russia in December in a prisoner swap for the American basketball star Brittney Griner, after months of negotiations between Moscow and Washington.

He wasted little time. Four days after returning home, he became a card-carrying member of Russia’s Liberal Democratic Party, known by its Russian acronym LDPR. It was founded by the nationalist firebrand Vladimir V. Zhirinovsky and, in Russia’s system of “managed democracy,” is nominally an opposition party but actually serves the Kremlin. The party specializes in flamboyant politicians who entertain and scandalize as much as they legislate.

More unassuming than flamboyant, Mr. Bout said he wanted to start his political career at the local level to gain a deeper understanding of his country after such a long absence. He gave few specifics about his campaign platform, nor did he provide evidence of any specific connection to Ulyanovsk, though it is common for parties to put forward candidates who have no connection to a region.

When you’re absent for 15 years from country, you need to start somewhere,” he said. “So for me, going into regional office, it’s a better way to understand the problems. I need to meet people. I need to learn how they live.”

As evidence of the consensual nature of Russian politics, he also praised improvements made to Moscow under the 10-year mayoralty of Sergei S. Sobyanin, who is expected to win a third term on Sunday.

“I returned to the Russia of my dreams — or even better than my dreams,” he said, saying Mr. Sobyanin had done a “perfect job” modernizing the city, introducing electric buses and boats and streamlining many public services on a smartphone app.

Mr. Bout said his process of reintegration into Russian society included simple things, like learning how to use a smartphone. He said he was “close to 90 percent” up to speed but conceded there are “still a couple of hiccups.”

His candidacy, if successful, would not be the first time that a figure accused of grave crimes by Western law enforcement found a role in government. Andrei K. Lugovoi, a former K.G.B. bodyguard accused by British authorities of murdering Alexander V. Litvinenko, a former K.G.B. and F.S.B. officer, is a member of Russia’s lower house of Parliament, the Duma, also for the LDPR. (Mr. Lugovoi has consistently maintained his innocence.)

Maria V. Butina, who pleaded guilty in 2018 to a single charge of conspiring to act as a foreign agent in a deal with federal prosecutors in the U.S., became a member of the Duma in 2021, for the United Russia party, whose de facto leader is President Vladimir V. Putin.

That Mr. Bout is running for such a low-level position is an indication that he lacks high-level political support from the Kremlin, said Andrei Pertsev, a political journalist with the independent news outlet Meduza.

“Bout was arrested in 2008, and in the intervening period, the leadership of the presidential administration changed several times,” he said. “The leadership of the Ministry of Defense and officials in charge of the defense industry have changed. For them, Bout is someone from the past.”

Still, Mr. Bout seems to have the support of some high-level officials in the Kremlin. In late July, he attended the Russia-Africa Summit meeting in St. Petersburg, an event important to Moscow’s continuing efforts to woo African leaders.

In the interview, Mr. Bout passionately defended his country’s policies, echoing a line among many pro-war elites that Russia’s true enemy is not Ukraine, and that it is actually fighting a larger proxy war with the West — one that the United States is doomed to lose.

He did not come across as a polished or natural politician. As he walked among a group of party activists fielding video calls Friday from LDPR election monitors across Russia, he did not interact much with team members, neither smiling nor shaking hands. Instead, he seemed stiff.

Since his return, Mr. Bout has spent a considerable amount of time traveling to Russian-occupied cities in Ukraine, opening up new LDPR offices in both the Donetsk and Luhansk regions, which were illegally annexed by Russia last year. He also traveled to Crimea with the LPDR leader Leonid Slutsky as part of a large delegation, and helped open a party office in Chechnya, a territory in the Caucasus region that fought two wars against Russia but is now run by a Kremlin loyalist.

There had been speculation in the Russian and Western press that with the death of the Wagner mercenary chief, Yevgeny V. Prigozhin, and the expected restructuring of the group’s lucrative operations in Africa, Mr. Bout’s reappearance in Russia could prove useful to the Kremlin. He acknowledged opening a business consulting company since his return, but he dismissed the possibility of returning to his old line of work — one he insisted against all evidence had been “totally focused on logistics, different than the sales of weapons.”

“I’m just trying to very critically approach my own skills and my own capacities right now,” Mr. Bout said. “Let’s be realistic,” he added, noting that even before his decade and a half behind bars, his businesses had been hard hit by sanctions. He said he was someone who had “very little of his business left, very little of my own life.”

He added that he had “nothing much left of any old contacts,” especially in Africa, where “the regimes are changing quicker than the weather sometimes.”

Mr. Bout met Mr. Prigozhin in June in Russia just days before the Wagner mutiny, which saw the group’s mercenaries take over a military base in southern Russia and march within 125 miles of Moscow. The two visited a factory producing armored vehicles for the military and then families of fallen Wagner fighters. Before Mr. Prigozhin’s death, Mr. Bout said that the Wagner boss had been among the people who helped most in securing his release, but said he couldn’t share the details because he was not himself “fully aware” of Mr. Prigozhin’s activities.

Mr. Bout declined to discuss whether exchanging him for Ms. Griner was a fair trade, and he seemed to show some sympathy regarding Ms. Griner’s arrest in Moscow for possessing a small quantity of marijuana oil.

“Does it really matter now?” he asked, adding that he is grateful for the exchange. “I don’t wish anybody to be locked up in a foreign country.”

At least two American citizens whom the State Department has classified as “wrongfully detained” remain imprisoned in Russia. Paul Whelan, 53, was arrested in 2018 on espionage charges and sentenced in 2020 to 16 years in prison. Evan Gershkovich, a reporter for The Wall Street Journal, was detained in March on espionage allegations that his employer and the Biden administration have dismissed as bogus. His trial has not yet begun, but Kremlin officials have said they are in contact with their American counterparts over the possibility of a prisoner swap.

“I also wish that countries stop playing and using their little system of, you know, entrapping the citizens of other countries,” Mr. Bout said. “That would be better. And if the United States will stop playing ‘hunting for the Russians,’ that definitely would be a very significant step.”