The construction of the bridge started in 2013 and it is projected to be opened at the end of May 2016.
President Recep Tayyip Erdogan, who was accompanied by Prime Minister Ahmet Davutoglu, Minister of Transport, Maritime Affairs and Communication Binali Yildirim and several other ministers, expressed pride in the project.
The bridge constitutes an essential part of an ongoing highway project linking the Istanbul, Bursa, and Izmir provinces.
The 433-kilometer-long (269 miles) motorway is expected to provide a direct connection from Istanbul and its surrounding provinces to the third and fourth largest cities – Izmir and Bursa respectively.
The motorway crosses through the "Osman Gazi" bridge in the Izmit province, southeast of Istanbul.
Travel time between Istanbul and the western Izmir province is expected to decrease to three-and-a-half hours from nine hours currently.
The entire project – of which the worth is estimated at $9 billion - is scheduled to be finalized in 2018.
"It will be among the first completed ones of Turkey's 2023 [vision] projects," Erdogan noted.
Davutoglu said it was a historic bridge boasting modern qualities and bridging the country's two largest ports, Istanbul and Izmir.
Numerous other mega projects, such as Istanbul’s third airport, are expected to contribute to the country's 2023 vision, a set of goals to be reached by Turkey for its centennial celebrations.