"Eric was taken ill in the late afternoon at the editorial offices," said Dreyfus.
Izraelewicz, who had taken the helm at the influential centre-left newspaper last year, was rushed to a Paris hospital but pronounced dead in the evening.
No cause of death was given.
"Tomorrow everyone at the paper will be in shock," said Dreyfus.
Izraelewicz was also on the boards of the weekly publications Courrier international, which translates and publishes articles from hundreds of overseas newspapers, and Telerama.
The Strasbourg-born newspaperman, who studied international economics, had previously run the Les Echos and La Tribune dailies.