Kadıköy Mesut Kösedağı announced on October 22, 2026, that he is leaving the Republican People’s Party to join Yeni Parti, accompanied by 30 of the district’s 36 municipal council members. The move establishes Yeni Parti’s first municipal administration in Istanbul following internal party disciplinary proceedings.
The announcement arrived through a video message published on social media, marking a definitive break for a municipal leader who spent more than two decades inside the Republican People’s Party. Kösedağı pointed to consultations with residents across local neighborhoods during a month-long disciplinary process as the driving force behind the decision to switch political homes (according to reporting by KARAR). The departure shifts the political balance in one of Istanbul’s most prominent districts and gives Yeni Parti under leader Özgür Özel its inaugural municipal foothold in the metropolitan area.
Disciplinary Process Precedes Municipal Shift in Kadıköy
The political realignment follows internal friction within the Republican People’s Party. Kösedağı, alongside Sancaktepe Alper Yeğin and Sarıyer Mustafa Oktay Aksu, was referred to the party’s disciplinary board on September 30, 2026, under a demand for outright expulsion and precautionary measures. The disciplinary actions came in the wake of leadership shifts following a court ruling reinstating former general chairman Kemal Kılıçdaroğlu in May, after which party management initiated expulsions targeting various former administrators, lawmakers, and local officials (as detailed by Diken).
YENİ bir başlangıç… pic.twitter.com/5Id3qAQojS
Reflecting on the 23 years spent inside his former party before the expulsion proceedings began, Kösedağı described a month of direct dialogue with local residents before settling on his next steps.
Dear residents of Kadıköy, as you know, last month I was referred to the disciplinary board with a demand for my definitive expulsion by the Republican People's Party, of which I have been a member for 23 years. The feedback I received from you on the ground over this past month has been very valuable to me. Whenever I went to every neighborhood, whenever I went to every street, I talked with you, I listened to you. Mesut
Council Majority Follows Kösedağı Into Yeni Parti Ranks
Crucially, the mayoral switch does not represent an isolated departure. Kösedağı confirmed that the vast majority of the municipal legislature chose to move alongside him, securing legislative continuity for the district administration under a new banner (Mansethaber noted the scale of the transition). Out of 36 total seats on the Kadıköy municipal council, 30 members joined the transition to Yeni Parti (according to Ekonomim).
We made this decision together with 30 of our 36 council members. From now on, we will continue to work together with you for our Kadıköy under the roof of Yeni Parti. May the path ahead of us all be clear. Mesut
Local Roots and Metropolitan Experience Inform Kösedağı’s Career
The transition places a seasoned local administrator at the helm of Yeni Parti’s early municipal expansion. Born in Istanbul in 1984, Kösedağı completed undergraduate studies in public administration at Eskişehir Anadolu University before earning a master’s degree in global cities and Istanbul studies from Marmara University in 2018 (as outlined in biographical records).
- Began political activity in 2000 within the Kadıköy youth branch, later serving as youth branch president and Istanbul provincial youth coordinator.
- Served as a municipal council member in Kadıköy and the Istanbul Metropolitan Municipality across the 2014–2019 and 2019–2024 terms.
- Acted as group secretary and spokesperson for the municipal assembly group, focusing on public transportation and transit policy.
- Secured election as Kadıköy Mayor in the March 31, 2024 local elections, achieving the highest vote share among Istanbul districts at 68.78 percent.
Kadıköy Belediye Başkanı Mesut Kösedağı, Yeni Parti’ye katıldığını açıkladı. Böylece Yeni Parti’nin İstanbul’daki ilk belediyesi Kadıköy oldu. pic.twitter.com/8yYxoy71Zk