He will start his new role on 1 October and report to Adam Pace, the managing director at Annalect. Pace joined OPera in 2008 from Omnicom's OMD.
Randall's remit will include negotiating digital media deals for Omnicom agencies, which include OMD UK, Manning Gottlieb OMD and PHD.
He has filled the Aegis Media role since 2008, having previously occupied senior digital media and press buying roles at the Aegis-owned Vizeum.
OPera launched into digital trading in 2006 to negotiate umbrella deals with major online media owners on behalf of Omnicom agencies.
Other UK-based Omnicom Media Group shops include M2M, Rocket, PHD North and Drum.Follow @nickbatten2