The global advertising network, owned by the Interpublic Group, has announced that Europe and Middle East CEO Hollingsworth, as well as Asia Pacific and Africa chief executive officer Ben Barnes, are leaving "to pursue other interests".
In addition, Gene Bartley, chief executive office of North America, is to retire next year.
All three roles will now be scrapped and replaced with a newly created post of president and CEO of FCB International, which will be filled by Rafael de Guzman, the group's Latin American president and CEO.
De Guzman will report directly to Blamer, who joined as president and CEO of FCB Worldwide in June and made the decision that the three senior roles were surplus to requirements.
Blamer said: "Old school agency networks and structures simply do not work any more. Agency networks need to adapt. The most significant element of this new structure is that it will allow us to target our resources close to where they are of most value to our global and local clients."
FCB has renamed its local offices global centres of excellence, initially including the UK as well as other European bases in France, Austria and Germany.
This latest move comes as Interpublic struggles to contain heavy losses and departing clients. This week, it posted a third-quarter operating loss of $96.8m and an organic revenue decline of 2.6%. Recent client losses across the group have included General Motors and L'Oreal.
De Guzman's previous senior roles have included vice-president of marketing operations for Motorola in Latin America. He has also held senior roles at Nike, Grey and JWT.
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