The Portuguese giants have officially confirmed the arrival of the former Standard Liege stopper, who has joined the club on a free transfer
The 24-year-old, who was released by Standard Liege this summer, has spent time with the Portuguese champions on a trial basis in recent weeks.
And the former Genk stopper will remain at the Estadio do Dragao for the next five years after signing a deal which will keep him at the club until 2018.
Bolat, who holds both Belgian and Turkish citizenship, has the distinction of being the first goalkeeper to score a Champions League goal during open-play after netting in the dying stages of Standard Liege's group game clash with AZ Alkmaar in 2009.
The Turkey international spent much of last season on the sidelines with a cruciate ligament injury, but managed 19 clean sheets from 52 appearances for the Belgian giants throughout the 2011/12 campaign.