The 25-year-old Turkey international has made 166 career appearances, keeping 53 clean sheets. Last season he was a key player for Fenerbahce as they won the Turkish Cup and finished second in the Super Lig. Bayindir is United's fourth summer signing, after Mason Mount, Andre Onana and Rasmus Hojlund. Upon signing, Bayindir said: "It is a huge honour to join Manchester United and become the first Turkish player to represent this incredible club."I have a passion for success, and I will give everything to help this special group of players to achieve our ambitions.
"I cannot wait to start working with such an experienced goalkeeping unit. We will support each other and drive high standards every day so that each of us is ready to perform whenever called upon."
John Murtough, Manchester United football director, said: "Altay is an excellent addition to our squad and adds further quality to our already strong group of experienced goalkeepers. "Having consistently performed at a high level in a strong European league, he has the qualities to support us in achieving our ambitions across all competitions this season and beyond."