Greece's state statstics agency said toda the economy contracted by 0.5% in the third quarter, when its EU partners threatened to throw the country out of the euro zone.
In a flash estimate, the Elstat agency also revised figures for the second quarter downwards to 0.4% from 0.9% previously, marking an end to two consecutive quarters of economic growth.
In an annual comparison, Greek output fell by 0.4% from the third quarter of 2014, it said.
The data is consistent with European Commission forecasts that Greece will fall back into recession in 2015 after a brief respite last year.
Although Greece had a record tourism year, the gains were lost to economic uncertainty as the leftist government of Alexis Tsipras clashed with international creditors in June and imposed capital controls.
The announcement comes as the government is trying to finalise a new batch of reforms with international creditors to unlock access to funds from a bailout agreed in July.
Officials are trying to bridge disagreements over Greece's treatment of non-performing loans and home foreclosures.