Polish archbishop Jozef Wesolowski, who was recalled to Rome last year amid claims that he sexually abused a number of children in the slums of Santo Domingo, was found guilty by the Vatican's Congregation for the Doctrine of the Faith and can no longer perform priestly duties.
It is the first time that a Vatican ambassador has been defrocked for sexual abuse. Wesolowski has two months to appeal.
Wesolowski, 65, had been ambassador to the Dominican Republic since 2008, but was recalled by Pope Francis last August following accusations of sexually abusing minors.
Vatican spokesman Federico Lombardi said the ex-cleric would be stripped of his freedom of movement.