The Toffees are believed to have paid an initial £35m for the 21-year-old – who has signed a five-year contract – with clauses that could make him the club’s record signing.
Everton boss Marco Silva was managing Watford when they signed Richarlison for £11.5m from Fluminense in 2017.
“I want to have a lot of success with Everton,” said Richarlison.
“I think it is going to be important for me to be with Marco Silva again. I will learn more because I am still learning as a player and I aim to develop and grow here.
“I developed really well with him while he was with me at Watford. It was really good working with him and one day I believe he can help me to be selected for Brazil in the full national team.
“Everton have put their faith in me and I intend to honour this shirt and demonstrate on the pitch why I came here. I want my dreams to become a reality here at one of the biggest clubs in England.”
Richarlison scored five goals in his first 12 Premier League matches but has not netted since November.
Silva has been keen to take him to Everton since he succeeded the sacked Sam Allardyce on 31 May.
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“Richarlison is a good player who will make our team and our squad more competitive,” said Silva. “The competition between our players is really important to me.
“The player himself is fast, strong, very good technically and he can play in three positions across the front line. He can also score goals.”
The Merseyside club’s record signing is Gylfi Sigurdsson, who joined from Swansea in August 2017 for £45m.
