Speaking at the inauguration ceremony, Erdogan said reopening of the Iron Church was an important message for the international community.
"I believe it is the responsibility of the state to ensure everyone can worship freely," he said, adding that Turkey has supported the restoration of more than 5,000 artifacts in the past 15 years.
The orthodox church, also known as St. Stephen Church, is located in the historic Balat neighborhood on the shore of the city’s Golden Horn.
It had been undergoing major restoration works for the last seven years, in a project co-funded by the Istanbul Metropolitan Municipality and the Bulgarian government.
Erdogan noted 14 places of worship had been restored in Turkey recently.
They include the Great Synagogue in the western Edirne province, the Aya Nikola Church in the western Canakkale province and the Syrian Catholic Church in the southern Hatay province.
Joint efforts for restoration
Also, the Armenian Protestant Church in southeastern Diyarbakir, the Fevkani Church in southern Gaziantep province, the Taksiyarhis (Aya Nikola) Church in western Balikesir province and the Aya Yorgi Church in Istanbul are among the restored places of worship.
"Iron Church is the final project -- the last example," he said.
Erdogan said Bulgaria has many Ottoman era architectures, such as mosques, bridges, and tombs which he said need restoration.
"We can take up the task of their restoration together -- for the conservation of common cultural heritage, exactly as we did for the Iron Church," he added.
Turkish Prime Minister Binali Yildirim called reopening of the church “the best example” of religious tolerance that Turkey had exhibited towards other religions.
“I hope this message will be heard and understood properly,” he said.
Speaking about the restored artifacts, he said 1,029 artifacts have been returned to 167 religious foundations.
Turkey's EU membership
Criticizing the lack of religious tolerance especially in Europe, Yildirim said: “The risk of religious and cultural polarization is increasing.”
Bulgarian Prime Minister Boyko Borisov, who also attended the ceremony, praised the restoration of the church, calling it "unique and magnificent".
“Our religion is being represented just beside the Golden Horn,” he said, referring to the primary inlet of the Bosphorus.
Speaking about Turkey’s EU membership process, Borisov said that efforts to normalize relations between Turkey and the EU in 2018 were needed. “We will contribute [to Turkey’s membership] as much as we can,” he added.
Bulgaria took over the rotating presidency of the Council of the EU as of Jan. 1.
Also attending the ceremony, Istanbul Mayor Mevlut Uysal said Istanbul hosts “thousands of precious historical artifacts just like Iron Church".
Istanbul contributed 13 million Turkish liras ($3.47 million) to the project which cost 16 million liras ($4.28 million), he said.
The church was built in 1898 from prefabricated cast iron elements after its former wooden structure caught fire.