Chuki is Bremen's fourth signing of the summer, following striker Kenny Quetant, defender Karlo Simic and midfielder Darwin Soylu. The club beat off interest from VfB Stuttgart, RB Leipzig, Como 1907 and Juventus to secure his signature.
The Valladolid academy product is primarily a number ten but is capable of playing on the flanks. He scored nine goals and contributed nine assists across 55 senior appearances for his hometown club, including a productive final season in the Spanish second division that yielded seven goals and eight assists in 34 appearances.
Valladolid were relegated from La Liga the previous season, with Chuki having made 18 appearances in the top flight.
Head coach Daniel Thioune said: "We're very happy to have Chuki on board. He is a really good footballer who has mainly played centrally in attack, but who can also appear on the wide positions. He has a good record for his age. I'm sure he will help us with his qualities."
Chuki described leaving his hometown as a difficult but deliberate decision.
"I am happy and convinced that Werder is the best possible club for me and the right step for my career. It was a very considered decision. It has been hard to leave Real Valladolid — the club of my life — because I grew up there, in my city, and I will always be infinitely grateful to them."