The deal had been mooted last week by the French press, but there were reports that it had been complicated by the fact that Havas' chairman Vincent Bollore and WPP are each interested in acquiring Aegis Group.
Gabriel Gaultier, who heads Leg, is set to be put in charge of Havas' Citroen creative account, which is currently held by Euro RSCG.
The car marque recently dumped Havas-owned Media Planning Group from its French media-buying business and gave the account to Omnicom's OMD.
In The Wall Street Journal, Gaultier described his unhappiness with being owned by WPP.
"For us, it is preferable to be in a French agency. We were never very well treated by WPP. They didn't know of our existence," he said.
Terms of the deal have not been disclosed.
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