The 20-year-old has signed a five-year deal with the club for a fee believed in the region of £500,000.
Reina found himself largely out-of-favour at Barca last season making just ten appearances and the recent arrival of Robert Enke from Benfica pushed him further down the pecking order at Camp Nou.
Barca had made Reina aware that his services were no longer required at the club and Villarreal swooped to sign him.
Reina was delighted to have secured a move to Villarreal with the opportunity of first team football.
"I think moving to Villarreal is a step I had to take, it's not a step backward but a step forward and I am excited because Villarreal is a great shop window," Reina told Marca.
"I have to admit they have made me a very good offer and the recognition they have given me was very important."
"They are a great club and I am going to make a huge effort to make people happy with me," said Reina.
Reina admitted it was a wrench to leave Barcelona after coming through the ranks at Camp Nou.
"They have been the club of my life, it is hard to leave because up to now I have never worn another team's shirt," added the young custodian.