Italian Sannino, who had been out of work since being sacked by Chievo in November, revealed on Tuesday that he was due to fly to England.
The Hornets have wasted little time in entrusting him with the task of replacing former Italy and Chelsea forward Zola, announcing the appointment on their website.
Sannino, 55, has spent 17 years coaching the likes of Siena, Palermo and Verona and brings assistant coaches Francesco Troise, Giovanni Cusatis and Paolo De Toffo with him to Vicarage Road.
Source: PA
Source: PA