The former France U21 international has followed Mauro Zarate in joining the Hornets, signing on loan from AC Milan until the end of the season
Watford have signed AC Milan forward M'Baye Niang on loan until the end of the season with a view to a permanent move.
The 22-year-old has made 18 appearances for Milan in Serie A this season, but, after seeing him score just three goals, the Italian club have opted to allow him to kick-start his career in the Premier League.
OFFICIAL: Watford sign Zarate
He has previously spent loan spells at Montpellier and Genoa during his career at San Siro.
Niang joins a Watford side enduring a poor fun of form under former Inter and Napoli coach Walter Mazzarri.
Watford are 14th in the Premier League on 24 points, eight clear of the relegation zone having failed to win in their last seven league outings.
The Frenchman's arrival follows that of Mauro Zarate, who joined Watford from Fiorentina on a two-and-a-half-year deal on Wednesday.