The 22-year-old is thrilled to be joining the Champions League winners and cited the brilliance of their new boss as a big reason for joining the club
The Spain international was heavily linked with Manchester United, but made the decision to join die Roten in order to continue learning from his former Barcelona coach.
“I am very happy. If there is one day in your life where you can be completely happy, then today is such a day. I am very happy to be at such a big club like Bayern Munich,” Thiago told the official club website.
“[What attracted me to Bayern was] the history of the club which has been one of the best in the world for many years.
"The team plays very nice football and I also believe the arrival of Pep Guardiola will give me an extra boost.
“We have known each other for a long time, he is a trainer who gives me great confidence. I am a big fan of his kind of football.
"There are few coaches in the world with his capabilities. He was certainly an important reason as to why I went to Munich.”
Thiago has completed his €20 million [£17.3m] switch and will now join Spain team-mate Javi Martinez at the Allianz Arena.
He added: “I spoke to him [Martinez] a bit and he told me only good things. Munich is a spectacular city with a great atmosphere and a great enthusiasm for football.
"I will go on this adventure with great pleasure and hope that I will play many games and hopefully repeat last season’s success.”