Grey shareholders were being offered $1,005 per share under the deal. The agreement, which will allow Grey to operate under its own name, calls for 50 percent of Grey shares to be exchanged for cash and 50 percent of Grey shares to be exchanged for American Depository Shares of WPP.

Grey chairman and chief executive Ed Meyer reportedly will continue with the agency for two more years, according to a report in The New York Times.

In addition to its roster of blue-chip consumers clients, including Procter & Gamble, 3M, Mars and Warner Bros., Grey also operates the full-service medical agency Grey Healthcare Group.