The fourth season of the historical drama television series premiered on 25 October 2017 and concluded on 6 June 2018.

It is believed that Ertuğrul is dead despite the truth being that he is actually captured by some slave traders.

Meanwhile, Emir Sadettin convinces Dündar, Ertuğrul's brother and the new Kayı Bey, into selling Hanlı Pazar and moving back to Gündoğdu's tribe but is stopped upon Ertuğrul's return and is forthwith banished.

The plan nearly works but Köpek is saved by the Sultan's wife, Mahperi Hatun and leads to an event turning Tekfur Ares, later killed by Noyan, into a Muslim.

After this, Ertuğrul faces the return of Noyan but is successful in defeating him and his devious sister, Alangoya, who attempted to kill Ertuğrul's son, Osman, who was born on the same day as his mother's death.