As announced on the Hornets' official website, the Frenchman, who scored seven goals for the club last season under both Marco Silva and Javi Gracia, sees his stay at Vicarage Road extended to 2023.
Doucoure was a major part of Watford's side last season, finishing as their top scorer as well as being named Player of the Season as well as Players' Player of the Season.
Watford chairman and CEO Scott Duxbury said, “I am delighted that Abdoulaye has shown his commitment to what we are trying to achieve by signing a new long-term contract with Watford Football Club.
“It has become perfectly clear that our ambitions as a club match Abdoulaye’s ambitions as a player, and we are looking forward to continuing to work together to reach our goals.”
Doucoure moved to the Premier League from Rennes back in 2016, before spending half a season on loan at Spanish side Granada.
The former France Under-21 midfielder then joined up with the Hornets at the beginning of the 2016/17 season, where he has gone on to become arguably the club's best player just a few years later.
All in all, Doucoure has made 62 appearances for the Hornets, scoring on eight occasions. At just 25 years old, there is plenty more to come.