The Brazil striker has penned a new contract to 2031.
Thiago has scored 17 goals in 26 Premier League games this season.
“It’s brilliant that Thiago has committed his long-term future to the club,” said Bees manager Keith Andrews.
“The connection that he has with his team-mates, the staff and the fans, as well as how much the club means to him and he means to us, is pretty evident for everybody to see.
“Again, it’s the person before the player. I love working with him and I’ve loved seeing his evolution as a player. How he plays is such a big part of how we play and what our season has been so far.
“He’s been a massive player for us, so it’s a contract he thoroughly deserves and I’m really happy that the club have been able to get it done.”
Thiago, himself, also said: “I love the club and the people in the club. It’s a true love, a real love.
“In the beginning, when I first came, I had the injury. The staff and the people around the training ground were helping me and supporting me.
“When the fans support me, and I see them singing my name and singing my song, it gives me more power. I’m really happy for all of the love they have given to me. It means so much.”