Barca agreed a deal to sign the Croatia midfielder from La Liga rivals Sevilla last month and the 26-year-old has now completed the formalities for his switch to Camp Nou for an undisclosed fee.
The Catalan giants confirmed on their website that Rakitic had come through a medical at their Ciutat Esportiva training ground and put pen to paper on a contract until 2019.
Rakitic, who insisted on Monday that he had not been signed as a replacement for Xavi and Cesc Fabregas, will wear the number four shirt in a new era under Luis Enrique.
Speaking at a press conference on Tuesday, Rakitic spoke of his determination to succeed at Barca after winning the UEFA Europa League with Sevilla last season.
He said: "I'd like to say thank you to the club for the way they have treated me over all these days. Like all footballers it's important to feel comfortable, knowing that people are counting on you.
"I'm here to help to rewrite history, last year at Sevilla we did that. It opened the door to me, I've got a lot of hunger.
"From first day Zubi (sporting director Andoni Zubizarreta) approached me I said yes. It was an incredible sensation and it was very clear from the start it was something I wanted to do. I now want to work hard and improve."
