A leading member of the now disbanded terrorist group November 17 returned to Korydallos prison on Thursday morning after a 48-hour furlough.
Dimitris Koufodinas had gone on a hunger strike for almost two weeks because authorities refused to give him a leave of absence from prison.
The prison leave, the third for Koufodinas, was widely criticized by the United States, the United Kingdom and Turkey, who condemned his temporary leave as unjust for his victims and their families.
November 17 is responsible, among others, for the murder of American, British and Turkish diplomats during its 27 years of activity.
The group, which first appeared when its members assassinated the CIA station chief in Athens, Richard Welch, in December 1975, remained elusive until 2002, until one of its members was arrested after a botched bomb attack that year.
Koufodinas is serving 11 life sentences plus 25 years for participating in 11 of the 23 assassinations perpetrated by N17.