After her successful performance as General Manager of Istanbul Ferry Lines, Dedetaş became a mayoral candidate for Üsküdar, the coastal district of Istanbul.
Dedetaş, who saved Haliç Shipyard, the oldest and most active shipyard in the world, from dying during his tenure as the general manager of Ferry Lines, also served as the chairwoman of the board of directors of TMMOB Chamber of Naval Engineers (GMO) for the 44th term.
Sinem Dedetaş became the first woman mayor of Üsküdar.
Before 2019, due to his opposition to the construction of a shopping mall at the Haliç Shipyard, the AKP IBB administration banned her from entering the facility.
In 2019, Ekrem İmamoğlu appointed Sinem Dedetaş as the General Manager of Ferry Lines, to which Haliç Shipyard is affiliated.
She increased the turnover of Haliç Shipyard from 1 million TL to 130 million TL.
