- Midfielder moves to Vicarage Road on season-long-loan deal
- He made 12 appearances for the Foxes in all competitions last year
The 24-year-old, who has played more than 80 times for the Foxes, has been with the Club since 2005 having joined the Academy at the age of seven.
After two loan spells with Burton Albion, Hamza made his City debut in 2017 and went on to help Leicester to three consecutive top-eight finishes in the Premier League in recent seasons.
He was also part of the team that lifted the FA Cup in May 2021 and was involved in European campaigns in 2020/21 and 2021/22, as the Foxes reached the last four of the UEFA Europa Conference League last term.
He will now link-up with the Hornets, who are next in action on Friday 12 August when they play host to Burnley (8pm BST kick-off).