Baxtiyar Haciyev (aka Bakhtiyar Hajiyev), a U.S. Harvard University graduate and member of the Positive Change movement, was arrested in March 2011, convicted, and sentenced to two years in prison for evading the compulsory military service required of Azerbaijani young men.
He has denied any violation of law.
Ahead of the appeal ruling, a group of Harvard University instructors sent a letter to Azerbaijani President Ilham Aliyev, urging Haciyev's prompt release.
International human rights watchdogs have also called on the Azerbaijani authorities to release Haciyev and other jailed opposition activists.
Haciyev's previous request for early release was rejected in December.