Apprehended soldier Sgt Vadim Shishimarin was sentenced for killing Oleksandr Shelipov, 62, in the northeastern town of Chupakhivka on 28 February.
He admitted to shooting Mr. Shelipov but stated he had been acting on rulings and asked forgiveness of his widow.
Multiple other apparent war crimes are being examined by Ukraine.
Moscow has banned its troops targeted civilians at the attack while Ukraine says at least 11,000 crimes may have occurred.
This trial in the Ukrainian capital Kyiv is being seen as Ukraine’s opportunity to demonstrate, beyond doubt, that a Russian soldier killed a civilian with no regard for the rules of war.
Ahead of the ruling, Shishimarin’s defense lawyer – set by the state – told BBC News no Russian official had been in touch with him. President Vladimir Putin’s spokesman stated the Kremlin had “no information” about this case.
At the time of the slaying Shishimarin, 21, and other fighters were crossing in a car they had seized after their convoy came under invasion and they became isolated from their unit.
When they stained Mr. Shelipov he was speaking on his phone, Shishimarin told the court. He says he was told to shoot him with an assault rifle.
His defense lawyer told the court on Friday that Shishimarin had only been released after twice rejecting to carry out the order to shoot and that only one out of three to four rounds had hit the target.
He said Shishimarin had removed the games out of fear for his own safety and he questioned whether the defendant had intended to kill.
At one dramatic point during the trial, the victim’s widow Kateryna Shelipova faced 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 reply to that. Requesting forgiveness of the widow earlier, he said: “But I understand you won’t be able to forgive me.”