Ms Ockrent's resignation came five months after a change in the magazine's ownership and a week after a statement by the new owners, part of the Havas group, that they wanted it to "become closer to the readers".
Although the author of the words, Christian Bregou, of CEP Communications, denied that his remarks implied a change of editorial direction - down- market and away from the political and foreign coverage Ms Ockrent had favoured - his comment was widely interpreted as a sign that Ms Ockrent's days were numbered.
In a letter to staff yesterday, she said: "It is clear that the owners of l'Express have a different vision of what the magazine should be."
In a radical redesign last autumn, Ms Ockrent introduced what was regarded at the time as a more "televisual" style. The changes were credited with increasing the magazine's readership by almost one-third. But the increase was not maintained, and year-end figures showed the left-of-centre Nouvel Observateur overtaking l'Express in domestic sales. Only l'Express's foreign sales kept it at the top.
While editorial and personal differences are the immediate reason for Ms Ockrent's departure, her resignation is also symptomatic of a gradual shift in the French media and business establishment as those associated with the political left give way to those more in tune with the prevailing political direction.
Although l'Express seems politically neutral, if anything slightly to the right, Ms Ockrent is associated with the left wing and is married to Bernard Kouchner, a former socialist minister and founder of Medecins Sans Frontieres.
The new director of l'Express is expected to be Denis Jeambar, former head of Europe 1 radio.