Captain Troy Deeney scored for the fourth consecutive game as he converted from the penalty spot in the first half before Odion Ighalo completed the win in injury time.
The Hornets moved up to ninth in the table while Norwich, with just one victory in their last nine league outings, are 16th.
Norwich skipper Alex Tettey returned to Alex Neil's starting XI after missing the 1-1 draw against Norwich with a groin problem.
Watford goalkeeper Heurelho Gomes, taken off on a stretcher with a neck injury at Aston Villa last weekend, lined up for the visitors.
On a cold and blustery day, it was Norwich, 3-0 winners both home and away against Watford in the Championship last season, who enjoyed the best of the early exchanges.
But as the half wore on, the hosts began to take a stranglehold on what was turning out to be a rather scrappy affair.
With 13 minute gone, Ben Watson took aim at the Norwich goal, but his 20-yard effort deflected off the heels of Sebastian Bassong for only a corner.
Seven minutes later, Ikechi Anya found space on the right-hand side, but his cross lacked any quality and went straight into the body of a grateful Declan Rudd.
But then, after half an hour, the breakthrough came
Etienne Capoue dispossessed a dithering Tettey and in his attempts to make amends for his error, the returning Norwich skipper hauled Ighalo down.
Referee Mike Dean immediately pointed to the penalty spot and Tettey was booked
It could, and probably should have been worse, with Ighalo denied a clear goalscoring chance
Deeney made no mistake from 12 yards to score his fifth goal in six games.
Watford upped the ante and Ighalo appeared to double his side's advantage with the interval approaching, but his effort - teed up by an Allan Nyom header - was ruled out for offside
Television replays suggested it was the wrong decision.
Shortly after half-time Nathan Ake, the on-loan Chelsea defender, was left flat out on the turf after a nasty collision with Andre Wisdom.
Norwich's Wisdom charged in for a header, but in the process wiped out Ake, who landed on his neck
Fortunately after several minutes of treatment, Ake was back on his feet and was able to play on.
With Dieumerci Mbokani now on for Nathan Redmond, Norwich appeared to carry a greater threat going forward and Mbokani perhaps should have hauled the visitors level
A free-kick from the left-hand side missed everyone, and fell to Mbokani, but the Congolese striker failed to make any significant contact and Gomes gobbled up the ball.
At the other end Ighalo fluffed his lines when put through by Etienne Capoue
Ighalo, a constant threat for Watford, then produced a fine save from Rudd who dived down low to his left before Bassong did enough to put Ighalo off his stride and the hosts were denied once more.
But in the 91st minute, Ighalo finally got the goal he deserved, holding off the challenge from Bassong, before slipping the ball under the legs of Rudd.
Source : PA
Source: PA