The 22-year-old playmaker completed his switch from Camp Nou to the Allianz Arena on Sunday for a fee believed to be around €20m (£17.3m).
Thiago revealed that he joined the European Champions after feelings of stagnation set in with the Liga champions.
"It has not been an easy decision. Barca has been my home. I made the decision because I needed a change of scenery," Thiago told reporters. "I've thought a lot, a lot. I have considered it a lot as last season was my last with Barca.
"From the outside it looks like a huge club, but when you walk inside that is when you really see its greatness. They have a great history.
"In the world there are few teams that can compete at the level Barcelona and Bayern are at. It is not an easy change because I am coming from a team I have been at for a long time. But it is greatly compensated because Bayern are a big club."
Thiago was part of the Spain Under-21 side that won the European Championships this summer.