The agencies will develop a multimedia campaign, which will highlight the website's "learn, chat and play with the pros" proposition.
The website allows gamers access to tips and advice from a number of respected professional poker players, including Andy Bloch and Chris Ferguson.
The work is set to break in spring 2006, and is expected to be rolled out across Europe later in the year.
The winning campaign was devised by the freelance creatives Paul Belford and Nigel Roberts alongside Naked Inside. It will include content, events, digital, outdoor and sponsorship elements.
FullTilt Poker was founded by Bob Wolf, the former chief executive of Chiat Day.
Commenting on the appointment, the CHI managing partner, Johnny Hornby, said: "We are delighted to have the man who ran Chiat Day for 13 years and presided over campaigns such as Apple's 'think different' as our client.
"Bob's pitch brief was testament to what we think working with FullTilt Poker will be like. He simply said 'show us your best work'."