The 21-year old midfielder becomes the seventh Spaniard on Swansea's books and is looking forward to joining fellow countrymen Michu, Chico Flores, Angel Rangel, Pablo Hernandez and summer signings Jordi Amat and Jose Canas at the Liberty Stadium.
"That will help me to settle quickly," he told the club's official website.
"I am very happy to have joined Swansea City. Since I've been a little boy it has been my dream to play in the Premier League.
"From the moment I heard of the interest from Swansea I have watched their games and followed the news at the club. The style of the team suits me, and so too does the style of the manager.
"I am looking to improve my English immediately as I want to communicate better with my team-mates. On the pitch I just want to give everything I have to the club in order to help the team this season."