Journalist Olivier Dubois, 48, was abducted by the Al-Qaeda-linked Group to Support Islam and Muslims (JNIM) in the northern Malian town of Gao in April 2021.
Based on French and Malian judicial documents from the probe, the report said a fixer working with Dubois had informed France's anti-jihadist Barkhane force of his plans to interview a jihadist leader.
Barkhane planned to track the leader back to his base but abandoned the operation last minute, it said.
But they did not deploy the necessary means to prevent the journalist from being kidnapped, it said.
But a diplomatic source said a letter had been sent to Dubois the day before he was kidnapped, formally advising him against making the trip.
In addition, Liberation - for whom Dubois was writing at the time - had refused to back his plan to interview the jihadist in view of the risks.
An internal army probe found in late 2021 that there had been "no personal fault within the Barkhane force" over the kidnapping.
But "the sensitivity of the topic was not sufficiently taken into account so as to allow... a dissuasive action with regards to the journalist," it said.
The report is published by newspaper Le Monde, with daily Liberation and broadcasters RFI and TV5Monde.
Dubois flew home to France in March, nearly two years after he was kidnapped.
Contacted by AFP, the French foreign ministry declined to comment due to the ongoing investigation.
The military general staff also declined to comment.
French forces withdrew from Mali last year following a fallout with the ruling junta.