Dentsu has confirmed that former UM CEO Fiona Johnston will become client chief from next month. 

Johnston, who oversaw a string of business wins at UM over four years, worked under Bass for half of that period.

The two also held senior positions at GroupM, where Bass was investment chief and Johnston formed a formidable partnership with then MediaCom boss Mark Pejic.

Bass is tasked with retaining Dentsu's media clients, the largest of which is Woolworths, and bringing in new business across a division that has undergone major change in recent years amid broader group surgery under outgoing CEO Angela Tangas.

Dentsu ANZ's new boss, former Accenture consultant Patricio De Matteis, starts in January.