Hoare has been charged with strengthening WPP's tenure of the HSBC business as the chief executive of "team HSBC". He has strong links with HSBC because Cordiant's Bates network handled the account in the key Asian market.
The announcement came as HSBC confirmed a global review of its marketing services.
Interpublic, Omnicom, Publicis Groupe and WPP will pitch in May.
Hoare's second role will be in an international capacity at WPP's J.Walter Thompson, based in London. However, he not yet finalised the details with the network's recently appointed worldwide president, Michael Maedel.
Hoare said: "I'm delighted to be joining JWT. It is a famous and highly respected global brand. It is an agency with talented people and a client list that offers great opportunities.
"I believe HSBC is a fantastic growth opportunity for the group and I will be working to develop that relationship," he added.
Hoare made a name for himself during a 14-year spell at Young & Rubicam, latterly as chief executive. His tenure came to an end when Y&R acquired Rainey Kelly Campbell Roalfe three years ago.
He moved to Bates as the UK group chairman before being promoted to Cordiant's executive committee and being named chairman of Bates in Europe, the Middle East and Africa.
But the beleaguered Cordiant was taken over by WPP last year and Bates UK subsequently closed its doors in December.
Chris Herd, the managing director of Bates UK, will not be joining Hoare at JWT. It is understood Herd had been lined up to run a WPP-owned agency in Australia but was unable to reach an agreement on terms.
Andrew Cracknell, Bates' former executive creative director, is not joining WPP either.
Maedel was not available for comment as Campaign went to press.