Opinion | The Kremlin is trying to kill Alexei Navalny. It should free him.

On top of the unjust 11½-year sentence he is currently serving, Mr. Navalny, 46, faces an upcoming trial for “extremism” that could result in an additional 30 years, according to his staff, and was recently told he will face yet another trial by military court on charges of “terrorism,” which could add 35 more years. “They have brought absurd charges against me,” he said in a video court appearance last week. “It looks like I face life in jail for that case.” In the extremism case, Mr. Navalny said he was given 196 volumes of trial materials and only 10 days to examine them, in prison.

Mr. Navalny, the target in 2020 of a failed assassination attempt by Russia’s security services using a Soviet-era military nerve agent, is struggling with severe health problems. An ambulance was called when he experienced stomach pains on April 7. Yet despite his fragile condition, he has been recommitted to solitary confinement every 15 days.

He has lost weight and his daughter, Daria Navalnaya, said her father is being tormented by prison authorities when he purchases food from the prison canteen. “Now, the situation has gotten so ridiculous that he buys the food which is, you know, oats — he buys the oats, the oats are brought to him, shown to him, and then are just destroyed. So, he can’t eat. And it’s, you know, something so basic is stripped away from a human being. It is outrageous,” she said, citing his lawyers.

In the letter to Russian President Vladimir Putin, some 130 leading writers, poets, filmmakers, playwrights and others demanded that “the torture of Navalny cease” and called for the jailed opposition leader to receive independent medical attention. The signatories include writers Margaret Atwood, Salman Rushdie and J.K. Rowling; dancer and choreographer Mikhail Baryshnikov; filmmaker Ken Burns; Nobel Prize winning authors Svetlana Alexievitch, J.M. Coetzee, Orhan Pamuk and Mario Vargas Llosa; biologist Richard Dawkins; actor Jude Law; and many others.

“Navalny is serving prison sentences based on charges which would never have been upheld under any independent legal system,” they wrote. Pressing Mr. Putin to release him, they added: “It is in your power.”

Mr. Navalny is a prisoner of conscience, of courage and of significance to the future of Russia. His freedom is urgent — and essential.