French public company Vivendi, which is chaired by Vincent Bolloré, is to buy the 60% of Havas that is controlled by his family company, Bolloré Group.
The €9.25-a-share deal for Havas, which was announced after the French stock market had closed, values the Bolloré Group’s 60% stake in the ad group at over €2.3bn.
The whole of Havas is valued at €3.9bn based on Vivendi's offer of an 8.8% premium over the value of the shares at the close of trading today.
The premium is 20.6% over the average Havas share price for the last 12 months, according to Havas.
Havas said part of the motivation for a sale is that it is "threatened by increasing competition from companies coming from other sectors" and maintained Vivendi "wishes to preserve jobs".
Vivendi, which is worth €24bn, will have majority control of Havas. Other shareholders can choose to sell to Vivendi, although Havas shares will continue to be listed on the stock market under the terms of the deal.
An acquisition of Havas has been rumoured for years and intensified in recent months as the ad group, which is led by Bolloré’s son, Yannick Bolloré, merged its media and creative divisions and a number of senior executives departed.
Havas said in a statement: "If Vivendi's offer is accepted, Vivendi would enter a new phase of development to accelerate its building of a leading world-class content, media and communications group and will ensure the newly created group a unique positioning in an environment in which content, distribution and communications are converging.
"If this transaction is successful, it would enable Havas to leverage Vivendi's skills in talent management, content creation and distribution. In return, Vivendi will gain access to Havas's expertise in consumer science, data analytics and new creative formats."
The statement continued: "Vivendi wishes to preserve jobs and to allow Havas to develop its business in an industry which is undergoing rapid consolidation and is threatened by increasing competition from companies coming from other sectors."
Universal Music is the world's biggest music company and Canal+ is a French pay-TV giant.
This is the second major advertising transaction in which Bolloré has been involved in recent years, and follows him selling his 26% stake in Aegis Group for a significant profit when Dentsu bought it in 2012.