Betfair has a long relationship with Powerscourt, going back to 2005 when the agency was hired to provide Betfair with advice on European taxation policies. The agency currently advises the gambling site on media relations and public affairs.
Betfair announced its intention to float while unveiling pre-tax profits of £18m and EBTIDA of £62.2m for its core business in the year to the end of April 2010.
The company will not issue any new shares, but the float will allow founders Ed Wray and Andrew Black to sell some of their holdings in the company. Around 10% of the company is expected to be sold by a number of its major shareholders.
The listing is expected to value the company at around £1.5bn.
Established in 2000, the site cuts out traditional bookmakers by allowing punters to match bets directly with each other.
Betfair said the listing would enable it to grow internationally, where its market presence is currently lower than in Britain.