Russia's Supreme Court has reduced former oil tycoon Mikhail Khodorkovsky's jail sentence by two months, paving the way for his release in August 2014.
Khodorkovsky, 50, was Russia's richest man as head of the Yukos oil company before his arrest in 2003 and sentencing in 2005 for tax evasion and fraud.
The court issued its ruling after considering a complaint by Khodorkovsky's lawyers that his arrest was illegal and the length of his prison sentence was unfair.
A court decision is also expected today on whether to cut the sentence of Khodorkovsky's former business partner Platon Lebedev.
Describing his case as political, he said earlier: "Faulty court rulings have already become a catalyst for the protest movement (against Putin). A growing part of society is demanding ... to be able to live and not be afraid.
"It always has been, and remains, important for me to get justice in my homeland", said Khodorkovsky, who is seen by some as a potential opposition leader.
Khodorkovsky's $40-billion (€30bn) business empire was broken up and sold off, mainly into state hands, after his arrest and subsequent sentencing in 2005.
He had fallen out with Mr Putin by funding political parties other than the main pro-Kremlin party and suggesting some oil deals involving the state were corrupt.
In their first trial, Khodorkovsky and Lebedev were sentenced to nine years in prison, later reduced to eight, for fraud and tax evasion. They had both pleaded not guilty.
More charges were brought against them and their sentences were extended until 2017 after they were found guilty of money-laundering and theft in 2010.
Their sentences were later reduced to 2016 on appeal and then to 2014.
Khodorkovsky was due for release in October 2014, and Platonov in July next year.
The European Court of Human Rights last month rejected suggestions that the case against Khodorkovsky had been politically motivated, but found that the initial trial was unfair and the 2005 sentencing was unjustified.