In a statement it said that Carlo Alberto Capella was ordered to face trail on Thursday, with the first hearing set for June 22nd.
Capella, who was in office until last year, was recalled from Washington by the Vatican in September.
The US State Department notified the Vatican in August through diplomatic channels of a possible violation of child pornography laws by a member of its diplomatic corps in Washington, the Vatican said at the time.
The United States had made "an official request" for the man's diplomatic immunity to be lifted but the Vatican refused, said a US official on condition of anonymity.
It is the latest case the Catholic Church has faced after repeated criticism for the way it has handled scandals over paedophile priests.
Last week Pope Francis wrote a letter to Chileans expressing "shame" that the Catholic church failed "to listen and react in time" to allegations of sexual abuse by the country's clergy.
The Chilean church has been rocked over accusations of wide-scale ignoring and covering up of child abuse by paedophile priest Fernando Karadima during the 1980s and 1990s.
In May the pontiff promised to "restore justice" after reading the conclusions of an investigation into the abuse, carried out after his defence of Chilean bishop Juan Barros -- accused of covering up Karadima's abuses -- caused a public outcry.
He later apologised to three of Karadima's victims at the Vatican and last weekend he received seven more people abused by the priest, who was suspended for life by the Vatican.
Two weeks previously 34 Chilean bishops announced their resignation over the scandal after being summoned to the Vatican by Francis.