The 24-year-old, who was detained on Sunday, was known to intelligence services for wanting to go to Syria to fight with jihadists.
"Several war weapons, hand guns, ammunition, bullet-proof vests and computer and telephone hardware" were found at his home and in his car, Interior Minister Bernard Cazeneuve said.
The arrest comes more than three months after Islamic extremists went on a three-day killing spree in and around Paris, leaving 17 people dead.
Cazeneuve told reporters that apart from the weapons, police had also discovered detailed research "clearly establishing that the person was planning to commit an imminent attack against one or two churches".
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"Sunday morning, this attack was foiled."
The suspect's alleged link to the mysterious murder of Aurelie Chatelain, an unemployed dance enthusiast, was not clear.
Her body was discovered on Sunday in her car in Villejuif, a town close to Paris. She had been shot three times.
Some nine hours later, her body was discovered by passers-by as smoke poured out of the car from an overheating laptop.
The car was parked in a turn in the road, on a hill, in front of another vehicle in a calm residential road.