Watford completed the £13 million signing of young Brazilian forward Richarlison from Fluminense on Tuesday.
Richarlison had already agreed a five-year contract and the 20-year-old is now able to join up with the Premier League club after a successful work permit application.
"Brazilian attacker Richarlison has signed for Watford on a five-year deal, the Hornets are delighted to confirm," the club confirmed on their website.
Richarlison, who watched Watford's friendly with Real Sociedad on Saturday, scored 19 goals in 67 appearances for Fluminense.
He becomes new Watford manager Marco Silva's sixth signing following the arrivals of Tom Cleverley, Nathaniel Chalobah, Kiko Femenia, Will Hughes and Daniel Bachmann.
The Brazil Under-20 international is expected to be in contention to make his debut in Watford's opening Premier League fixture against Liverpool at Vicarage Road on Saturday.