Hartmann had argued the documents should have been made available during a separate trial at the International Court of Justice in which Bosnia unsuccessfully tried to sue Serbia for genocide.
But the tribunal ruled that it had the right to prevent documents from being leaked and that Hartmann, as a permanent employee, was fully aware of the court's rules and procedures.
"It is necessary to discourage the accused or any person from disclosing confidential information in future," said presiding Judge Bakone Moloto.
The precise content of the documents has never been made public, but they are thought to chronicle contacts between the Serbian government and the Bosnian Serb army.
Hartmann maintained they could prove a link between Belgrade and war crimes committed in Bosnia - most notably the massacre of up to 8,000 Muslim men and boys at the Bosnian village of Srebrenica in 1995.
Critics of the case say that such papers should never have been the subject of a confidentiality order in the first place.
The French journalist had faced a maximum sentence of up to seven years in jail or a fine of almost £90,000 ($150,000).
Her defence counsel said other journalists had written about the documents before her publications and that her case was merely intended to set a legal precedent.
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