Mikhail Khodorkovsky, a former oil magnate and a prominent Kremlin critic, has been released from jail in the wake of a decree issued by Russian President Vladimir Putin.
Khodorkovsky flew to Germany on Friday after his release, the prison service said. The German Foreign Ministry confirmed he had landed in Berlin.
"After his release, he flew to Germany, where his mother is undergoing treatment," the Federal Service for Execution of Punishment (FSIN) said in an official statement posted on its website.
The decree pardoned Khodorkovsky after spending more than a decade behind bars for embezzlement, fraud and tax evasion.
"Guided by humanitarian principles, I decree that Mikhail Borisovich Khodorkovsky... should be pardoned and freed from any further punishment in the form of imprisonment. This decree comes into force from the day of its signing," said the decree signed by Putin and published by the Kremlin.
The Russian president had revealed his decision to pardon Khodorkovsky during his annual press conference on Thursday, saying the former head of oil giant Yukos had requested a pardon because his mother was ill.
In comments broadcast on state television, Putin said it was the first time his foe had made such a request.
Khodorkovsky said in a statement after his release from prison that he had sought a pardon from Russian president and did not admit his guilt.
Khodorkovsky, 50, used his estimated fortune of $20bn to support communist and liberal opposition to Putin prior to his arrest in 2003, when he was snatched off his corporate jet by special security forces.
Khodorkovsky also challenged Kremlin interests by lobbying for the construction of a Yukos-controlled oil pipeline to China that would compete with the interests of state energy firms.
He and his business partner, Platon Lebedev, were convicted of fraud and tax evasion in 2005.
A second trial ended in 2010 with an embezzlement conviction for both men.
Putin did not comment on the fate of Lebedev, but the president's spokesman Dmitry Peskov said he had not asked for a pardon.
Khodorkovsky had been due to be released in August 2014.
Analysts viewed the pardon, along with an amnesty for two jailed members of the Pussy Riot punk band and the 30-member crew of a Greenpeace protest ship, as a measure aimed at easing international criticism of Russia's human-rights record ahead of February's Winter Olympics in the city of Sochi.