The male stray gained fame this month after barking menacingly as part of a pack of dogs at European and International Monetary Fund austerity inspectors driving up to the Finance Ministry for talks.
Ruby was later captured by municipal officials and freed Friday after being observed for two weeks and showing no signs of aggressiveness.
A city statement said Ruby's detention followed a complaint that he bit a man, and wasn't linked with the ministry incident. Dogs often follow anti-austerity protesters in Athens.
Recession-crippled Greece is being kept afloat by international bailouts, released following regular assessments of demanded cutbacks and reforms.