Simunek's promotion means he oversees the majority of Grayling's activity across Europe, with Central and Eastern Europe, Russia, CIS, Germany, Austria and Switzerland already under his remit.
Grayling’s UK chief Alison Clarke will continue to run operations in the UK and Ireland.
Simunek has worked for Grayling for almost 20 years and was promoted to the role of European chief executive in June 2013.
Grayling appointed Simunek to its international board in 2014 and he will continue to work alongside Clarke, Grayling chief executive for Middle East, Turkey & Africa Loretta Ahmed and Grayling US chief executive Peter Harris.
Paul Taaffe, chief executive of Grayling’s parent company, Huntsworth, said that Simunek had a track record of connecting clients with the best talent regardless of their location.
Simunek's plan is to integrate teams across Europe.
He said: "I am a big believer in the power of regional networks and intend to run Continental Europe on the basis of ‘micro-regions’, each of which will be connected together through one regional structure."
The appointment comes as both Grayling and its parent company, Huntsworth, are going through turbulent times.
Huntsworth reported a pre-tax profit drop of 20 per cent in 2014 with revenue falling by £6.4m to £164.7m.
The global PR group also had to swallow an impairment charge of £65m relating to Grayling, where chief executive Pete Pedersen resigned at the start of 2015.