Rebbouh and Kemoun left Carat's parent company, Aegis Media Europe, where they were the joint chief executives, last November. They were pursued by several advertising networks.
They have launched KR as a Paris-based holding company, said to be partly backed by French venture capitalists, to house their ventures. The first of these is likely to be a stake in the media company Press Informatique, a company that manages the majority of subscriptions in France.
Observers suggest the pair are holding discussions with Fabrice Larue, the former president of DI Group, the media arm of Louis Vuitton Moet Hennessy, about taking a stake in Press Informatique. Larue already owns 34 per cent of the business but is said to have ambitions to replace Le Monde as the majority shareholder.
However, the pair are also expected to look at providing media planning and buying services. They are hiring senior staff from rival agencies.
Rebbouh and Kemoun were close to clients including Renault and Carrefour while they were at Aegis. They left after clashes with Aegis' chief executive, Doug Flynn, over company strategy.
Rebbouh and Kemoun's careers have moved in tandem, from founding a media company called 2010 Medias with Carat France in 1985, to selling it to Aegis in 1991.
A year later, they joined the board, becoming the joint chairmen of Carat France in 1995 and then the joint chief executives of Aegis Media Europe.