Russia's Supreme Court has ordered the release of Platon Lebedev, the former business partner of Mikhail Khodorkovsky, with whom he was jailed in 2005.
Platon and Khodorkovsky were convicted of tax evasion and theft after funding opposition parties and falling out with President Vladimir Putin.
Mr Putin pardoned Khodorkovsky last month, but Lebedev, who was due for release in May, did not seek a pardon and stayed in jail.
The Russian Supreme Court ruled that his sentence should be reduced and that he would be able to walk free on Friday.
"Release Lebedev," Supreme Court Judge Pyotr Serkov declared in the ruling, after reducing his sentence so that it amounted to time served.
Both men's convictions remain in place, despite repeated appeals.
It did not change a court order under which Lebedev and Khodorkovsky must pay 17bn roubles ($500m; £300m) in tax arrears.
That debt is an obstacle to Khodorkovsky's return to Russia after leaving for Germany in December.
The releases are believed by many to be part of a drive to improve Russia's international image ahead of the Sochi Winter Olympics next month.
Other prominent inmates freed in the past few weeks included two women from the Pussy Riot protest group, jailed over the performance of a "punk prayer" critical of Putin in a Russian Orthodox church.
Mr Platon used to head NFO Menatep, while Mr Khodorkovsky ran oil giant Yukos and was once Russia's richest man.
Khodorkovsky and Lebedev were regarded by human rights groups as political prisoners but the Kremlin denies using the courts for political purposes.