Caught trooper Sgt Vadim Shishimarin was sentenced for killing Oleksandr Shelipov, 62, in the north-eastern town of Chupakhivka on 28 February.
He conceded shooting Mr Shelipov however said he had been following up on orders and requested pardoning from the man's widow.
Numerous other affirmed atrocities are being examined by Ukraine.
Furthermore, in a contention where the intentional focusing of regular citizens has become one of the characterizing highlights, Monday's result starts a critical lawful trend.
Moscow has consistently denied its soldiers have designated regular folks, in spite of an abundance of proof going against the norm, while Ukraine expresses in excess of 11,000 violations might have happened.
Ukraine, be that as it may, is probably going to bring more cases like this to unpick Moscow's sweeping disavowals.
This condemning is probably not going to prompt a quick change in strategies from the attacking powers, yet it presents to Oleksandr Shelipov's widow Kateryna Shelipova equity.
Might Putin at some point be arraigned?
Forcing the lifelong incarceration, Judge Serhiy Agafonov said Shishimarin, 21, had completed a "criminal request" by an officer of higher position.
"Considering that the wrongdoing perpetrated is a wrongdoing against harmony, security, mankind and the worldwide lawful request... the court doesn't see the chance of forcing a [shorter] sentence of detainment," he said.
Shishimarin, wearing a blue and dark hooded pullover, watched procedures quietly from a built up glass confine the court and showed no feeling as the decision was perused out.
His legal counselor said an allure would be held up against the decision.
The Kremlin's reaction is now moving, with regulations being drafted and courts being set up in Russia to attempt a few Ukrainian detainees as war hoodlums.
This proposes the two nations could before long end up in a legitimate blow for blow while the contention seethes on.
Shishimarin served in Russia's Kantemirovskaya tank division. At the time of the killing, he and other soldiers were travelling in a car they had seized after their convoy came under attack and they became separated from their unit.
When they spotted Mr Shelipov he was speaking on his phone, Shishimarin told the court. He said he was told to shoot him with an assault rifle.
His defence lawyer told the court on Friday that Shishimarin had only fired after twice refusing to carry out the order to shoot and that only one out of three to four rounds had hit the man.
He said Shishimarin fired the rounds out of fear for his own safety and he questioned whether the defendant had intended to kill.
In one dramatic moment, the victim's widow Kateryna Shelipova confronted Shishimarin. "Tell me please, why did you [Russians] come here? To protect us?" she asked, citing Russian President Vladimir Putin's justification for the invasion of Ukraine.
"Protect us from whom? Did you protect me from my husband, whom you killed?"
The soldier had no answer to that. Asking forgiveness of the widow earlier, he said: "But I understand you won't be able to forgive me."
Ms Shelipova told the BBC: "I feel very sorry for him but for a crime like that - I can't forgive him."
Since President Putin sent Russian troops into Ukraine on 24 February, at least 3,838 civilians have been killed and 4,351 injured, according to the UN.
Among the dead are numerous suspected victims of war crimes in occupied towns such as Bucha.
Earlier this month, the BBC obtained CCTV footage of the killing of two civilians in cold blood allegedly by Russian soldiers, a case now being investigated by prosecutors as a suspected war crime.
