Midfielder Ben Watson admits he jumped at the chance to join Watford's promotion push, after joining from Wigan.
West Brom have completed the signing of Callum McManaman from Wigan for an undisclosed fee.
The 36-year-old striker joined Rovers on a two-year deal from Braga last summer but found first-team opportunities hard to come by last season, making just eight league starts amid a total of 20 appearances which brought four goals.
With boss Gary Bowyer unable to guarantee Gomes more playing time next term, the two parties have agreed to go their separate ways.
"Nuno is a model professional, who has been a fantastic influence on the younger players at the club and has been a pleasure to work with," Bowyer told the club's official website.
"I fully understand that at this stage in his career he wants to play regular football, but unfortunately I can't give him those guarantees.
"I spoke to Nuno about the situation and we have agreed to terminate his contract so that he is free to source other options in order to prolong what has been a long and distinguished playing career. I thank him for his dedicated services and wish him all the best in the future."
Gomes' four goals came in successive matches within his first six games for the club at the start of last term having been signed by Steve Kean.
Yet Kean's departure last September saw opportunities dry up for the former Portugal international under subsequent managers Henning Berg, Michael Appleton and Bowyer.
Gomes said: "Playing for this historic club has been an absolute pleasure. Despite only being here for a year, I have enjoyed my time here immensely.
"I want to say a big thank you to Gary, the staff, the players and, most importantly, the fans for making me feel so welcome. I will look out for Blackburn's results and I hope they can achieve their goal of getting back into the Premier League."