Dimitris Koufontinas, a senior member of the November 17 terrorist group, will be granted a 48-hour furlough on Friday, the second in the space of three months.
Koufontinas was jailed for life over the killings of 11 people including US, British and Turkish embassy staff.
His first 48-hour leave from Korydallos prison in 15 years last November was greeted by dismay by the families of his victims.
It also sparked criticism from the US and Britain.
US ambassador to Greece Geoffrey Pyatt has said at the time that it was an insult to victims and their families.
“I add my voice to those from across Greece’s political spectrum deploring prison council decision to release a convicted terrorist, murderer & N17 leader,” Pyatt had said on Twitter.
British ambassador Kate Smith likewise tweeted London’s “profound disappointment” and added that the embassy “shared” the pain of the victims’ families.