Monsignor Carlo Capella was a senior official in the Vatican's Washington embassy before being recalled last year.
The priest was the subject of investigations by the Vatican and in the United States and Canada. He has been in Vatican custody since April.
He was recalled after the US State Department notified the Vatican of a "possible violation of laws relating to child pornography images" by a diplomat in Washington.
In a statement on Saturday the Holy See said a formal investigation had been closed and Msgr Capella had been summoned to trial, with the first hearing scheduled for June 22.
It said the alleged offence was the possession and exchange of child pornographic material, "with the aggravating circumstance of the large quantity involved".
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