The WPP bid is worth 555p a share and values Tempus at £437m.
The question now is whether WPP CEO Sir Martin Sorrell will brave the markets and push ahead with the deal.
WPP already owns 26% of Tempus. The majority of its stake was built up earlier this year when it acquired 22% of the media-buying firm for an average price of 220p a share. It bought a further 4% in the firm earlier this week for 555p a share.
If WPP goes ahead with the bid, it plans to merge its The Media Edge media-buying unit with the Tempus-owned CIA.
In its offer document, WPP said it believes that there are significant strategic and financial benefits in the combination of these businesses, beyond those achievable through a combination of CIA and The Media Edge.
The combination of CIA and The Media Edge will create the world's fourth-largest media-planning and buying network worldwide, with combined annual billings in excess of £10bn.
Havas shares remain unchanged from earlier this morning, when its shares were down 9.7% to €6.46 (£4.08). WPP was down 6.6% to 453.5p, having opened this morning at 500p. Tempus shares have fallen sharply, dropping 14.4% to 472.5p, having opened this morning at 556p.
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