The 23-year-old has signed a four-and-a-half-year contract and will wear the number 33 shirt.
Upon signing for the Blues, Emerson said: "I came here because it's a great team with a great history. Today I am realising one of my dreams to pull on the shirt of such a great club.
"English football is something I have been watching since I was 15 years old. It is a really beautiful game over here but it is going to be even more beautiful to play it."
Chelsea director Marina Granovskaia added: "We are delighted to welcome Emerson to the club.
"He is a young and talented player who strengthens the squad and will provide excellent competition for places as we pursue success in three different competitions."
Source: www.chelseafc.com