The business, Global Counsel LLP, will be chaired by Lord Mandelson and run by former Number 10 aide Ben Wegg-Prosser. In recent weeks, Mandelson has been working out of JWT’s London offices.
It is understood that Global Counsel will initially advise foreign companies, due to Cabinet Office restrictions, although this could change.
The move strengthens the link between Lord Mandelson and WPP. The group has a minority stake in CHI & Partners, of which Lord Mandelson was a director.
Sir Martin Sorrell declined to comment.