"A natural cause of death, due to a cardiac event, is confirmed," a statement from the Church said following the passing of Jozef Wesolowski, 67, on Friday.
The former papal envoy to the Dominican Republic was to be tried for alleged sexual abuse of minors but his hearing had previously been halted due to bad health.
Wesolowski was the senior Vatican official in the Dominican Republic at the time the offences were said to have taken place.
He was recalled to Rome in 2013 after rumours of alleged abuse surfaced. He was then defrocked in 2014 and placed under house arrest.
Vatican spokesman, Fr Ciro Benedettini, said the ex-archbishop's funeral would be held on Monday at the Vatican.
He said no press would be allowed to attend the funeral or wake.
His body will then be taken to his native Poland for burial, Fr Benedettini added.