Russian opposition politician Vladimir Kara-Murza was found guilty on charges of treason and denigrating the military by a court in Moscow on Monday.
The critic of President Vladimir Putin was sentenced to 25 years in prison.
Kara-Murza voiced the opposition slogan "Russia will be free" in court after the sentence was announced.
It's the harshest sentence of its kind since Russia criminalized criticism of its military soon after its invasion of Ukraine last February.
His lawyer, Vadim Prokhorov, told DW that "considering his health conditions it is effectively a death sentence."
After the trial, the court said that it found Kaza-Murza guilty of spreading "false" information about the military and of being affiliated with an "undesirable organization."
Germany, UK, EU, UN condemn ruling
A German Foreign Ministry spokeswoman said "we condemn this judgment in the strongest possible terms," and that it showed "the shocking level repression has now reached in Russia."
UN High Commissioner for Human Rights Volker Turk appealed for Kaza-Murza's release.
"Kara-Murza was tried on charges that appear related to the legitimate exercise of his right to freedom of opinion ... no one should be deprived of their liberty for exercising their human rights, and I call on the Russian authorities to release him without delay," Turk said in a statement.
The "outrageously harsh court decision clearly demonstrates yet again the political misuse of judiciary in order to pressure activists, human rights defenders and any voices opposing Russia's illegitimate war of aggression against Ukraine," the EU's top diplomat Josep Borrell said in a statement.
The British government called the verdict "politically motivated" and said it had summoned the Russian ambassador to make clear it believed it contrary to Russia's international obligations on human rights, including the right to a fair trial.
Who is Vladimir Kara-Murza?
Vladimir Kara-Murza is a 41-year-old former journalist and prominent opposition politician who holds Russian and British passports and once studied at the University of Cambridge.
He spent years lobbying foreign governments to impose sanctions on Russia and individual Russians for purported human rights violations. He had close links to Boris Nemtsov, a leading opposition figure assassinated near the Kremlin in 2015.
Russian state prosecutors secured their desired maximum 25-year sentence on charges including treason and discrediting the Russian military by criticizing what the Kremlin refers to as its "special military operation" in Ukraine.
In his final speech to the court before Monday's verdict, Kara-Murza compared his trial to one of Josef Stalin's show trials in the 1930s and to later Soviet-era cases. He declined to ask the court to acquit him, saying he stood by and was proud of what he had said.
"Criminals are supposed to repent of what they had done. I, on the other hand, am in prison for my political views," Kara-Murza said. "I also know that the day will come when the darkness over our country will dissipate."
'Running away would be a gift to the Kremlin'
Kara-Murza's supporters say the father of three and 2022 Vaclav Havel Human Rights Prize winner has survived two past attempted poisonings but Russian authorities deny any involvement in any alleged attacks. His lawyer Maria Eismont says he suffers from a serious nerve disorder as a result.
"Vladimir is sadly very ill, because he has survived two poisoning attempts," Kara Murza's lawyer Vadim Prokhorov told DW on Monday. "Under the conditions in the detention facilities in the northwest of Moscow his illness has deteriorated. It's clear that considering his health conditions it is effectively a death sentence."
Prokohorov said that a high-security jail could be lethal and called for international efforts to secure Kara-Murza's release.
Kara-Murza was charged last October after giving critical speeches at public events internationally, including in Helsinki, Lisbon and Washington.
Speaking to DW in late 2021, Kara-Murza compared his case with that of fellow jailed and poisoned opposition figure Alexei Navalny and said that he had no intention to leave Russia, although he had arranged for his family to do so.
"Running away would be a gift to the Kremlin," he said. "That's exactly what they want. And, once political activists leave the country, they lose the moral right, the moral authority, to continue their work."
