The 30-year-old full-back will move to Vicarage Road on an initial one-year deal but Watford also have the option to make the move permanent.
Zuniga, who has made 62 appearances for his country, joins the likes of Isaac Success, Christian Kabasele and Jerome Sinclair as new signings at Watford this summer
Having started his career with Atletico Nacional in his homeland, Zuniga moved to Italian side Siena in 2008 before joining Napoli a year later for 8.5million euros.
He spent seven years at Napoli, four of which were under the guidance of new Watford head coach Walter Mazzarri, and helped them win the Coppa Italia in 2012 and 2014.
Zuniga was on loan at Bologna for the second half of last season.
Source : PA
Source: PA