When asked upon his sentencing before a Russian military court in Rostov-on-Don on August 25 whether he understood the charges against him, he and co-defendant Oleksandr Kolchenko, who received a 10-year sentence, sang Ukraine's national anthem. On November 24, he declined to testify.
"I have nothing to say," Sentsov said at the hearing before the Russian Supreme Court in Moscow. "This is a dull television show."
WATCH: Oleh Sentsov And Oleksandr Kolchenko Sing Ukraine's National Anthem Upon Being Sentenced In August
Sentsov, a native of Crimea, was arrested in May 2014 on suspicion of planning the fire-bombings of two pro-Russian organizations.
After being convicted on August 25, the 39-year old said that a "trial by occupiers cannot be fair by definition."
The Supreme Court on November 24 upheld the 10-year sentence of co-defendant Kolchenko as well.
The prosecution of Sentsov and Kolchenko has been widely criticized as retaliation for their outspoken opposition to Russia's annexation of Crimea.
A UN resolution overwhelmingly asserted in 2014 that the peninsula remained part of Ukraine, although Russian authorities have installed their own institutions and exercise day-to-day control.
Kyiv and NATO have also accused Russia of direct military intervention in eastern Ukraine, where fighting between Ukrainian forces and pro-Russian separatists has killed more than 7,900 people since April 2014.
Sentsov is an internationally acclaimed film director whose first feature film, Gamer, about a computer-game-obsessed teenager, was presented at the Rotterdam Film Festival in 2012.
EU lawmakers in September urged Russia to release Sentsov and Kolchenko, calling their detentions a "blatant violation of the territorial integrity of Ukraine" through "illegal kidnapping."
Icons of European cinema last week made a public plea to famed Russian film director Nikita Mikhalkov, a staunch supporter of Russian President Vladimir Putin, to lobby for Sentsov’s release.
"It is our responsibility -- as filmmakers and as human beings -- to stand up for human rights and the freedom of speech. Please raise your voice and support us in our support of Oleg Sentsov," prominent members of the European Film Academy wrote to Mikhalkov in the November 20 letter.
The four signatories included Polish directors Agnieszka Holland and Andrzej Wajda, as well as German filmmakers Wim Wenders and Volker Schloendorff.
Separately, legendary Polish actor Daniel Olbrychski last week published a letter addressed to Mikhalkov in the Polish daily Gazeta Wyborza, writing: "I believe that you do not think and feel differently [from] all the great artists from many countries who signed letters regarding our Ukrainian colleague to President Putin."
"The cruelty of [the] trial brings to mind the darkest judgments of the past of our common civilization and culture. I appeal to you and I beg you, as your Polish brother, to do something. Among all of us, you are the person closest to your president and the case," Olbrychski wrote.