If the merger passes muster with shareholders and government officials, the new conglomerate’s combined revenues, which totaled $22.7 billion last year, would be far greater than the $16 billion in revenues for WPP of London, the current industry leader.

Publicis is considered a French national champion, and French officials have been active during President François Hollande’s tenure about protecting its business icons from foreign dominance. It was not immediately clear what position Mr. Hollande’s government might take on the merger. Calls to Élysée Palace over the weekend were not returned.

At a news conference, Mr. Lévy said the companies informed the French government of their plans on Saturday and had received “tremendous support” from officials. “We are not owned by the French government,” Mr. Lévy said, “yet we are one of the iconic companies in France.”

He said that the combined companies wanted a neutral third country as the place to register the new holding company. They ruled out Ireland and Luxembourg, Mr. Lévy said, to avoid the appearance that they were seeking a tax haven. They chose the Netherlands — which at 25 percent has a nominal corporate income tax rate that is higher than Ireland’s, but below the 33.33 percent rate in France and the 40 percent rate in the United States, according to the global accounting firm KPMG. Mr. Lévy said the companies would keep their headquarters in both Paris and New York to avoid the impression that Publicis would be “swallowed” by an American company — something that he said would not be accepted in France.

In a statement, Mr. Lévy cited technological advancements in advertising and the rise of so-called Big Data — the ability to amass larger volumes of consumer information and make money from it in various ways — as reasons for the merger.