Other jury members for the festival, which will be held from 15 to 21 June next year, will be announced over the coming few weeks.
The Australian-born Davis joined JWT in 2003 and was promoted to his current position two years ago. Before joining JWT, he spent four years at Saatchi & Saatchi in Singapore and then Hong Kong. He was a judge at Cannes Titanium in 2006 and also guest-edited this year's Gunn Report.
Commenting on his appointment, Davis said: "Great creativity can and does come from anywhere. What I love about Cannes is that it recognises this truth across multiple disciplines on a scale unmatched by any other awards festival. It's an honour to be leading the search for the world's best creativity in film and press advertising in 2008."