WPP has sold a 49.9pc stake in PR agency Finsbury in a buyout deal that will make former People's Vote boss Roland Rudd chairman of the new venture.
The deal means the advertising group will merge Finsbury with German agency Hering Schuppener Consulting and Washington DC lobbyist Glover Park Group.
WPP, which owns all three firms, will remain the majority shareholder in newly formed Finsbury Glover Hering with a 51.1pc stake, while the new combined management team will acquire the rest.
Financial details of the transaction were not disclosed.
Alexander Geiser, managing partner at Hering, will become chief executive of the group, with Mr Rudd becoming co-chairman alongside Glover Park founder Carter Eskew.
The combined group will be launched in early 2021 with its headquarters in New York.
It will aim to take on rivals such as Brunswick and Teneo, vying to advise the biggest clients in the world of crisis management, dealmaking and lobbying.
The new venture will also give Mr Rudd, brother of former Home Secretary Amber Rudd and one of the best-connected executives in the City, a chance to move on from the fiasco he left behind at the pro-EU People's Vote campaign.
The former Financial Times journalist stood down as de facto chairman of the campaign last November after a row exploded over whether it should unequivocally back a remain vote if a second EU referendum took place.
Mr Rudd founded Finsbury in 1994 before selling it to WPP in 2001 for an estimated £60m.
Meanwhile, former Labour MP and shadow business secretary Chuka Umunna will join communications company Edelman to run its environmental, social and governance consultancy in a move first reported by the Financial Times.