Craig Dawson has left West Brom to join Watford on a four-year contract in a deal worth £5.5m.
The defender, who passed a medical on Saturday, has an option to extend his contract by a further year.
Centre-back Dawson has agreed a four-year deal at Vicarage Road to become the Premier League club's first summer signing.
The 29-year-old scored three times in 45 appearances in all competitions for the Baggies last season as they reached the Sky Bet Championship play-off semi-finals.
'The club wishes Craig and his family all the very best in the future,' read a statement on West Brom's website.
Dawson joined West Brom from Rochdale in 2010 but initially remained on loan at Spotland.
The former England Under-21 international, who had a temporary spell with Bolton in 2013, played 225 times for the Baggies, scoring 15 goals.