The CEO role is newly created, following the expansion of the PHD Network in Australia, reports Campaign Asia.
Coad left OMD at the end of 2009 to take up the position of CEO of CHE, a Clemenger Group creative agency. He said that while he loved the challenge of running a creative agency, he missed the media agency side.
He said: "When this opportunity came up – working with people who I know, trust and have great respect for – it was a no-brainer."
The role will encompass the PHD Sydney operation, and will include the recent successful launch of PHD Melbourne, set up to handle the A$120m (£79m) global ANZ media account.
It also includes responsibility for the Foundation business, a media activation joint venture business between Clemenger Group and Omnicom Media Group.
Barry Cupples, CEO, Omnicom Media Group APAC, said Coad's return was a "real coup" for the media industry.
"He is a world-class talent and we welcome him home with open arms. Truly, great news for PHD and the wider Omnicom Media Group network," Cupples said.