Brendan McAtamney is to step down from his role as chief executive of UDG Healthcare with immediate effect.
This follows the conclusion of the acquisition of UDG Healthcare by Clayton Dublier & Rice for £2.61 billion.
Brendan McAtamney has been CEO of UDG Healthcare since 2015.
Mr McAtamney will continue in a non-executive capacity with both of UDG Healthcare's two divisions.
Ashfield, UDG's global healthcare services business, will combine with an existing CD&R portfolio company Huntsworth to create a global leader in advisory, marketing, public relations and medical communications.
Its Sharp business, a global leader in contract packaging, clinical, manufacturing and technology services business, will run separately.
"I am honoured to have led UDG over the last six years and am thankful to have been supported by enormously talented colleagues across the globe," Brendan McAtamney said.
Over the years, collectively, we have generated excellent value for our shareholders but most importantly we have helped our clients provide innovative solutions to our shared patients," he said.
"I firmly believe UDG Healthcare, and its divisions of Ashfield and Sharp, have a very exciting future under the new ownership of CD&R and I look forward to supporting in a non-executive capacity," he added.
UDG, which has its headquarters in Dublin, specialises in healthcare advisory, communications, commercial, clinical and packaging services.
It has strong market positions in the pharma services space and it employs around 9,000 people in 29 countries.