State prosecutors, who had requested the court jail him for 25 years, had accused him of treason and of discrediting the Russian military after he criticised what Moscow calls its "special military operation" in Ukraine.
In a CNN interview broadcast hours before he was arrested, Kara-Murza had alleged that Russia was being run by a "regime of murderers."
He had also used speeches in the United States and across Europe to accuse Moscow of bombing civilian targets in Ukraine, a charge it has rejected.
I also know that the day will come when the darkness over our country will dissipate," he had said.
Kara-Murza's lawyers say that as a result, he suffers from a serious nerve disorder called polyneuropathy.