Tonic, founded by former BBJ planning directors Geoff Seeley and Tim Elton, has been hired to handle the £4m business for the UK launch of Ultimatebet.com, one of the United States' largest online poker sites.
Meanwhile, Experience, set up by former Zenith Optimedia and Mediaedge:cia bosses Greg Turzynski and James Whitmore, along with former Mediaedge:cia strategist David Reid, has been awarded the £1.5m strategic account for PokerStars.
Tonic's Seeley said: "The online gaming market is exploding in the UK and Ultimate Bet has got the vision to capitalise on it. It's an environment currently dominated by bland, generic activity and we're looking forward to shaking it up a bit."
Whitmore, of Experience, said: "Poker Stars' reputation for innovation and bravery is nothing short of unique in an otherwise relatively homogenous category".
The online gaming business has seen huge expansion in the UK over recent years. In 2004, the total global revenue from online gambling was £6.6bn according to market research group Mintel.
Tonic's client list includes Yeo Valley Organic, EasyJet, Interoute and Scottish Media Group. Experience has handled briefs for The Independent , JC Decaux and Tesco.