Karamanlis repeated his country's support for Turkey's bid to join the European Union (EU) and said the pipeline would improve stability in the region.
Greece and Turkey, still divided over territorial disputes in the Aegean sea and Cyprus, agreed in 2004 to build the 285km-long natural gas pipeline between Karacabey in northern Turkey and Komotini in Greece.
It will carry about 12 billion cubic metres (bcm) of gas a year - three bcm for Greece and the remainder for re-export to Europe - from the Shah Deniz field in Azerbaijan.
The EU supports the project as it looks to diversify its energy suppliers and reduce its dependence on Russia, from where it buys about a quarter of its gas.
Erdogan said: "Turkey is moving fast to become the fourth energy supply route for natural gas to western Europe. There is a mutual dependence in energy policies which will help create a favourable atmosphere."
Greece is already pressing ahead with an extension to the pipeline that will run from its west coast, under the Adriatic sea to Italy, giving central Europe access to natural gas from the Caspian sea by 2012.
A much bigger pipeline, the Nabucco, backed by the EU and also designed to ease the bloc's dependence on Russian gas, is still in the planning.
It will cut through the Balkans to Austria.