A woman's body was found in the house in Magnanville, northwest of Paris, where the man had been holed up for hours, interior ministry spokesman Pierre-Henry Brandet said.
A three-year-old boy was found in the house "in shock but unharmed," a prosecutor added.
Police sources had told the media earlier in the evening that the attacker had taken the policeman's wife and son hostage in their home after repeatedly stabbing the officer outside around 9.00 pm (local time).
Loud detonations had been heard at the scene as officers from France's elite RAID unit moved in.
Neighbours calling police claimed they heard the man chanting Islamist slogans, Reuters France reported.
"The negotiations were unsuccessful -- a decision was made to launch an assault" around midnight, interior ministry spokesman Pierre-Henry Brandet said.
RAID officers said they "found the body of a woman" in the house and "the attacker was killed."
The prosecutor in the Versailles area outside Paris said the little boy was receiving medical attention.
Interior Minister Bernard Cazeneuve expressed his "infinite sadness" at the death of the police officer and his partner.
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