The Belgium international rejected the opportunity to move to Old Trafford in favour of joining "one of the biggest clubs in the world"
New Red Devils boss Louis van Gaal made the former Arsenal captain his primary summer transfer target but the versatile centre-back rejected the chance to move to Old Trafford in favour of a switch to Camp Nou.
"The decision was easy," Vermaelen told reporters at a press conference on Sunday. "It's one of the biggest clubs in the world.
"Everyone wants to play here and it's no different for me. That's why I chose this club."
Vermaelen added that he was drawn to Catalunya by the prospect of playing alongside some of the most famous names in world football, including the Blaugrana's star summer signing, Luis Suarez.
"He's a great player and he has made unbelievable steps in his career," the defender said of his former Ajax team-mate. "Everyone knows his qualities.
"As a person, I know him from Ajax and my experiences with him are very good. He's a very nice person.
"I didn't speak to him before I came here but I'm looking forward to meeting him.
"But I think the players who are here are great players. I have seen them play for the last two years. They have world-class defenders and there's lots of competition.
"But I'm very excited and it's down to me to show I can play for this club."
Vermaelen admitted that he is not yet back to full fitness after his exploits at this summer's World Cup with Belgium, but feels that he has plenty to offer the Blaugrana, who have made a point of addressing their longstanding defensive deficiencies this summer.
"I haven't trained with Arsenal, so I need some weeks to get fully match fit," he explained. "We'll discuss that [on Monday] with the club staff so we'll see how long I need to get fit.
"But I'll try to give my aerial strength to the club. I'm used to playing in the Premier League, with a lot of physical strikers and a lot of long balls.
"It's not going to be a surprise for me when teams play long balls."