The 27-year-old center-half signed a five-year contract with the Hornets and becomes the latest new addition to Vladimir IviÄās squad.
Troost-Ekong has spent the past two years in Italy with Udinese, playing 66 times for the Serie A side since his arrival from Turkish SĆ¼per Lig outfit Bursaspor in 2018.
Born in the Netherlands, he began his senior career in the Eredivisie with Groningen and Dordrecht before spells in Belgium and Norway, with Gent and Haugesund respectively.