The fullback has penned terms to 2026 with Barca and is now with Celtic on-loan for the season.
"I am very excited, it is a fantastic opportunity to come to this historic club," Valle said.
"They have given me a lot of trust, so I will try to do my best to pay it back. I've heard a lot about the fans and what we can experience in this stadium, so I'm just excited to experience it in real life."
Celtics manager Brendan Rodgers also said: "We are delighted to have Álex on this season-long loan as we continue to strengthen the squad for this season. His style of football will complement our attacking play and give us more options in our back line.
"Álex has been brought up in a real high quality football environment and learned all the good habits and skills associated with any top team. He is a player with some fantastic qualities."