The 23-year-old has signed a four-and-a-half-year contract and will wear the number 33 shirt.
Emerson, who began his career at Santos in Brazil, arrived in Serie A on loan at Palermo in August 2014.
"Speaking to the official club website, the Italian said: "'I came here because it's a great team with a great history.
'English football is something I have been watching since I was 15 years old.
The arrival of Emerson comes after fellow full-back Kenedy left for Newcastle on loan, while Chelsea are also sanctioning a temporary move for Baba Rahman to return to Schalke 04. "It is a really beautiful game over here but it is going to be even more beautiful to play it", he added. "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".