Then war started last month, President Volodymyr Zelensky of Ukraine tapped Mykhailo Fedorov, deputy prime minister, for a key role.

Fedorov, 31, the youngest member of Zelensky’s cabinet, immediately took over a parallel strand of Ukraine’s defense against Russia. He started a campaign to rally the support of multinational companies to separate Russia from the world economy and to isolate the country from the global internettargeting everything from access to new iPhones and PlayStations to Western Union and PayPal money transfers.

To achieve isolation from Russia, Mr. Fedorov, a former tech entrepreneur, used a combination of social media, cryptocurrencies and other digital tools. On Twitter and other social media, he pressured Apple, Google, Netflix, Intel, PayPal and others to stop doing business in Russia. He helped form a group of volunteer hackers wreak havoc on Russian websites and online services. His ministry also established a cryptocurrency fund which has raised more than $60 million for the Ukrainian military.

The job has made Mr. Fedorov one of Mr. Zelensky’s most visible lieutenants, deploying technology and finance as modern weapons of war. In effect, Mr. Fedorov is creating a new military conflict playbook that shows how an outgunned country can use the Internet, cryptography, digital activism and frequent posts on twitter to help undermine a foreign aggressor.

In his first in-depth interview since the invasion began on February 24, Fedorov said his goal was to create a “digital blockade” and make life so unpleasant and inconvenient for Russian citizens that they would question the war. He praised the companies that had pulled out of Russia, but said Apple, Google and others could go further with measures such as shutting down their app stores in the country altogether.

A technology and business lockdown, he said, “is an integral component to stopping the aggression.”

Fedorov, speaking via video link from an undisclosed location somewhere in Kiev, also downplayed concerns that his actions alienated urban Russians who might be the most likely to oppose the conflict.

“We believe that as long as the Russians remain silent, they will be complicit in the aggression and murder of our people,” he said.

Mr. Fedorov’s work is not the only reason why multinational companies like Meta and mcdonald’s they have withdrawn from Russia, with the human cost of the war provoking horror and outrage. Economic sanctions from the United States, the European Union and others have played a central role in isolating Russia.

But Peter Singer, a professor at the Center on the Future of War at Arizona State University, said Fedorov had been “incredibly effective” in asking companies to reconsider their connections to Russia.

“No celebrity, let alone a nation, has ever been more effective than Ukraine in calling corporate brands to name and shame them into acting morally,” Singer said. “If there is such a thing as ‘cancel culture,’ the Ukrainians can claim to have perfected it in war.”

In the 45-minute interview on Zoom, Mr. Fedorov, dressed in a baggy gray fleece with black zippers, sat facing a wood-paneled wall. He has slept three to four hours a night, he said, often interrupted every 30 minutes or so by alerts on the iPhone he keeps next to his bed. He said he was worried about his father, who had been in intensive care for the past week after a missile hit the house next door.

“I have brushed against horror,” he said. “The war has also knocked on my door personally.”

Mr. Fedorov grew up in the small town of Vasylivka in southern Ukraine, near the Dnieper River. Before entering politics, he founded a digital marketing company called SMMSTUDIO that designed online advertising campaigns.

The job led him to work in 2018 with Zelensky, then an actor who was making an unexpected run for the presidency of Ukraine. Mr. Fedorov became the campaign’s digital director and used social media to portray Mr. Zelensky as a youthful symbol of change.

Then Mr. Zelensky was elected in 2019, he appointed Mr. Fedorov, then 28, minister for digital transformation, putting him in charge of digitizing Ukrainian social services. Through a government app, people could pay speeding tickets or manage their taxes. Last year, Mr. Fedorov visited Silicon Valley to meet with leaders like Tim Cook, CEO of Apple.

After Russia invaded Ukraine, Fedorov immediately put pressure on tech companies to withdraw from Russia. He made the decision with Zelensky’s backing, he said, and the two men speak every day.

“I think this election is as white as it is black,” Fedorov said. “It’s time to take sides, either on the side of peace or on the side of terror and murder.”

On February 25, he sent letters to Apple, Google and Netflix, asking them to restrict access to their services in Russia. Less than a week later, Apple stopped selling new iPhones and other products in Russia.

The next day, Mr. Fedorov tweeted a message to Elon Musk, the founder of Tesla and SpaceX, requesting help in obtaining Starlink satellite internet systems made by Mr. Musk’s company, SpaceX. Technology could help Ukrainians stay online even if Russia damaged the country’s main telecommunications infrastructure. Two days after contacting Musk, a shipment of Starlink equipment arrived in Ukraine.

Since then, Mr Fedorov said he has periodically exchanged text messages with Mr Musk.

Fedorov also had a call last month with Karan Bhatia, a vice president at Google. Since then, Google has made several changes, including restricting access to certain Google Maps features that Fedorov said were security risks because they could help Russian soldiers identify crowds of people. The company has since suspended sales of other products and services as well, and on Friday blocked access to Russian state media globally on YouTube.

Fedorov has exchanged emails with Nick Clegg, head of global affairs for Meta, which is the parent of Facebook and Instagram, about the unfolding war.

Apple, Google and Meta declined to comment. Musk did not respond to a request for comment.

Public shaming has been effective, Fedorov said, because companies are “both emotional and rational in making decisions.”

But while many companies have stopped doing business in Russia, more could be done, he said. Apple and Google should remove their app stores from Russia, and software made by companies like SAP was also being used by dozens of Russian companies, she noted.

In many cases, the Russian government is isolating itself from the world, even blocking access to Twitter and Facebook. On Friday, Russian regulators said they would also restrict access to Instagram and called Meta an “extremist” organization.

Some civil society groups have questioned whether Fedorov’s tactics could have unintended consequences. “Shutdowns can be used in tyranny, not in democracy,” the Internet Protection Society, a Russian internet freedom group, said in a statement earlier this week. “Any sanctions that cut off the Russian people’s access to information will only strengthen the Putin regime.”

Mr. Fedorov said that it was the only way to galvanize the Russian people into action. He praised the work of Ukraine-supporting hackers who have been loosely coordinating with the Ukrainian government to attack Russian targets.

“After cruise missiles started flying over my house and over the houses of many other Ukrainians, and also things started exploding, we decided to fight back,” he said.

Fedorov’s work exemplifies Ukraine’s do-whatever-it attitude against a larger Russian army, said Max Chernikov, a software engineer who supports the volunteer group known as the Ukraine IT Army.

“He acts like every Ukrainian, doing the best he can,” he said.

Mr. Fedorov, who has a wife and a young daughter, said he was hopeful about the outcome of the war.

“The truth is on our side,” he added. “I’m sure we’re going to win.”

Daisuke Wakabayashi and mike isaac contributed report.