Italian Prime Minister Silvio Berlusconi will also attend the ceremony, as Italy's ENI oil company was a key partner in construction of the pipeline together with Russia's Gazprom.
The $3.2 billion Blue Stream project is the world's deepest underwater pipeline.
The official inauguration today at Durusu, near Samsun, comes two years after gas began to flow through the pipeline.
Since then, the project has been mired in corruption allegations in Turkey.
In a meeting with Erdogan today, Putin is expected to discuss bilateral trade relations and further energy cooperation.
Russia now supplies 60 percent of Turkey's gas and 20 percent of its oil.