His appointment ends a global search for a replacement for Rob Dow, who opted to retire earlier this year.
It also comes less than two months after Mather abruptly quit his long-time roost at The Campaign Palace.
Mather's resume features wins from virtually every major advertising award show.
In both 1995 and 1997 he was voted creative director of the year by Australia's foremost business magazine, BRW, and has represented Australia as a juror at Cannes and Clio - the world's two largest award shows.
In 2001, Mather was elected chairman of the jury at Clio, the first Australian ever to be selected.
Grey Global Group chairman Paul Gardner said Mather was an obvious choice.
"The decision became easy when Ron came on to the market," Gardner said.
"His unquestionable talent, experience and enthusiasm for the role made him an obvious choice."
The move caps a string of recent senior signings at Grey Australia, including the promotion of Jane Emery from general manager to managing director and Randal Glennon's appointment as general manager.
Mather, who started this month, said he needed little convincing to take the post.
"I'd planned to take a bit of a break but when I first met with Paul and heard the plans for the agency I just wanted to be a part of it," Mather said.