The indictment accused Paolo Gabriele, the butler under arrest at the Vatican since May, of grand theft.
While the Vatican had insisted throughout the investigation that Gabriele was the only person under investigation, the indictment also orders trial for Claudio Sciarpelletti. He is a layman in the Secretariat of State office and is charged with aiding and abetting Gabriele.
The scandal has embarrassed the Vatican, exposing infighting at high church levels, primarily involving Italian prelates.
The Vatican has promised a public trial. No date was immediately announced, but officials said it would be no earlier than late September. The Vatican tribunal returns from summer recess on Sept. 20.
Judge Piero Antonio Bonnet ruled that there was no evidence to indict Sciarpelletti -- a computer expert in the secretary of state's office who knows Gabriele -- on a charge of revealing secrets and insufficient evidence for a charge of grand theft.
There had been widespread speculation about the possibility of a mole in the secretary of state's office since some of the leaked documents seemed aimed at casting doubt at Cardinal Tarcisio Bertone's ability to be the Vatican's No. 2 as secretary of state.
Gabriele, who is married, lives with his family in Vatican City. After several weeks in isolation in a Vatican security cell, he was released to house arrest over the summer.
Sciarpelletti's office was searched on May 24, hours after Gabriele's arrest, Vatican spokesman the Rev. Federico Lombardi told reporters.
Sciarpelletti was arrested and spent one night in a Vatican security cell, but was quickly released when it appeared clear that his role wasn't a key one in the case, Lombardi said. The Vatican had steadfastly insisted the only known suspect was Gabriele.
"You can't speak of an accomplice in any way, but he was an acquaintance who could help Gabriele" in the butler's activities, Lombardi said. The indictment noted that in Sciarpelletti's desk was found a plain white envelope, sealed, with "Personal P. Gabriele" on the front and with the Secretariat of State's stamp on the back.
Sciarpelletti has been suspended, with pay, from his job, the spokesman said.
If Gabriele is convicted a sentence could run from one to six years, Lombardi said. But that depends "on any possible pardon" from the pope, the spokesman added.
"It's premature to speak of this now," Lombardi said of the possible criminal sentence.