Filmmaker Oleg Sentsov called for the release of other Ukrainians held by Moscow as he was set free Saturday in a historic prisoner swap with Russia.
"I am hoping that the rest of the prisoners will be released soon," the 43-year-old said after arriving at Kiev's Boryspil airport from Moscow.
He flashed a victory sign as he disembarked from an Antonov plane.
Sentsov, who was the subject of a star-studded international campaign calling for his release and received the European Parliament's 2018 Sakharov Prize, was one of 35 people released by Russia as part of the swap. The prisoner exchange also included 24 sailors.
"I want to say a big thank you to all those people who helped us, and our families," he said, adding that even if all Ukrainian prisoners were released, "our fight" would still not be over.
"The enemy is strong and is not going to give up but victory will be on our country's side," said the activist who was dressed in a black T-shirt.
"Glory to Ukraine!"
Sentsov's cousin Natalia Kaplan said she was overwhelmed.
"I don't believe it," said Kaplan, who had waged a high-profile campaign, to get Sentsov released.
Speaking to AFP, she called his release "a weight off my shoulders.
"I can finally get on with my life," she said.
Russia has not officially released a list of people who came home as part of the exchange.
Ukraine has said Russia is holding dozens of Ukrainians in its prisons.
Sentsov was arrested in 2014 and had been serving a 20-year sentence in an Arctic penal colony for planning "terrorist attacks" in Crimea.
While in jail, he refused food for 145 days to push for the release of all Ukrainian prisoners.
The film-maker is best known for his film Gamer, which screened to critical acclaim at the Rotterdam Film Festival in 2012.
Supporters had waged a star-studded global campaign to win his release, staging protests in dozens of cities in Europe, the United States and the Middle East.
Scores of celebrities took part, including bestselling US author Stephen King and Hollywood actor Johnny Depp.
European Parliament president David Sassoli welcomed news of Sentsov's release with "relief" and said he looked forward to welcoming him at the parliament to hand him the Sakharov prize which he had been awarded in absentia.