The 26-year old French midfielder has signed a four-year deal at Vicarage Road for a fee of £6million after spending the past two years at
White Hart Lane.
Capoue arrived at Spurs from French side Toulouse in 2013 and made 24 appearances in the Premier League.
He was delighted to make his new home in Hertfordshire with the Hornets who are preparing for life back in England's top flight.
"Hello Watford fans, I'm very happy to join the club now, I'm honoured," Capoue told the club's official website from the training ground.