She was reported to have returned to her Beijing home by September 2017.
Photographers caught up with her in Helsinki, where she was in transit, and she grinned widely for the cameras spreading her arms - a stark contrast from the few images of her that have surfaced over the past few years in China.
China's Foreign Ministry later confirmed her departure saying she left the country "by her own free will" for medical treatment, without specifying the ailments, according to spokeswoman Hua Chunying.
Berlin and other Western governments have been pushing for China to allow Liu to leave the country ever since her husband died of liver cancer a year ago this month.
Liu's release coincides with a visit to Germany by Chinese Premier Li Keqiang.
Ms Liu's departure was "wonderful news" but harassment of her family remained a risk to her freedom to criticise China, Amnesty International's China researcher Patrick Poon said. Liu Xia has never been charged with any crime.
Johnny Lau, a political commentator in Hong Kong, said he believed the authorities had let Liu Xia go to avoid her case sparking a "surge" of pressure on China around the July 13 anniversary of Liu Xiaobo's death.More news: President Trump announces Supreme Court pick
"I want to marry that enemy of the state!" she said shortly before the pair Wednesday in 1996 during Liu Xiaobo's stay at a labour camp, according to a biography of the dissident by Yu Jie.
Poon noted that with her brother still in China, Liu may find it hard, even risky, to speak about her case from Germany. The last time a famous political prisoner was permitted to leave China was in 2012.
Several people expressed concern about Liu's brother, Liu Hui, who was accused of fraud and sentenced to jail.
Liu Xia's release and her departure from the country show that sustained worldwide pressure can bring about positive human rights developments in China, Human Rights Watch said. A chair sat empty for him at the ceremony in Norway.
He died last summer of late-term liver cancer after the Chinese government repeatedly denied his request to receive medical treatment overseas. After the doctors determined Liu was "fit for travel", the Chinese government restated its previous position that he was too ill to travel overseas for treatment.
Liu Xia was seen getting into a vehicle soon after she got off the plane. Chinese officials told reporters she was free to do what she wished, but Western diplomats and the press were effectively banned from visiting her.
"While precise details of Liu's flight out of China are unknown, the only Finnair flight that left Beijing Capital International Airport bound for Berlin on Tuesday morning was Flight AY86, which took off at 10.55am, according to the airport's website".More news: Winners and losers of Trump’s decision to halt ObamaCare payments
Occasionally, she managed to make contact with friends and supporters.
Liu is a poet and artist.
"Too solitary", the note read, "I have not the right to speech / To speak loudly / I live like a plant / I lie like a corpse".
And in May, dozens of the world's leading writers and artists, from Michael Chabon to Paul Auster and Khaled Hosseini, called on China to release her to seek medical treatment overseas.
"I've got nothing to be afraid of".
"I'm so excited, I'm so excited, I don't know what to say", the Chinese poet and painter told AFP over the telephone that October.
"Xiaobo is gone, and there's nothing in the world for me now", she continued. "Dying is easier than living - there is nothing simpler for me than to protest with death".More news: Thailand football team won't attend World Cup final
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