Watford held on for their first victory in 12 matches, since beating Manchester United 4-1 in November.
Villa blow up a dominance but Watford grabbed all three points when Emmanuel Dennis powered home Ismaila Sarr’s 78th-minute cross after an opportunistic counter-attack.
It ended the visitors’ four-game goal drought and lifted them up to 18th in the Premier League.
The victory moved Watford to the top of the relegation zone, though still four points behind 17th-place Newcastle.
Villa will take on Brighton next Saturday, while Watford will host Crystal Palace on Wednesday.
