Dolma Kyab, 39, was freed last week after being convicted a decade ago of "endangering state security," the International Campaign for Tibet said late yesterday.
Tibet is tightly controlled by China's ruling Communist party, which is intolerant of public opposition to its policies, and often jails dissidents.
Kyab's trial happened in secret in Tibet's capital Lhasa and only came to light after a letter he wrote while incarcerated was smuggled out of prison months after his 2005 sentencing.
He added that authorities believed his writing was "connected to Tibetan independence".
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In his book, Kyab wrote about conceptions of Tibetan identity as well as Tibetan hopes for exiled spiritual leader the Dalai Lama to return to his homeland, the ICT said.
In it he told his "Tibetan brothers and sisters: We live in a time of national devastation. We have weathered countless years of darkness, countless dark nights."
China, which has ruled Tibet since the 1950s, has been accused of trying to eradicate its Buddhist-based culture through political and religious repression and large-scale immigration by Han Chinese.
Beijing says that Tibetans enjoy extensive freedoms and that it has brought economic growth to the region.
Tibetan spiritual leader the Dalai Lama fled Tibet after an abortive uprising in 1959 and established a government-in-exile in Dharamsala in India.
After his release from the Qushui Prison in Lhasa, Kyab was taken back to his home town, where family and friends draped him with white blessing scarves, ICT reported.