Gibraltar-based Cassava Enterprises, which is rebranding itself as 888.com, said Bell Pottinger was brought in to handle communications around the float last month.
BPC&F managing director Anne-Marie Wilkinson and account director Nick Lambert are leading the account.
HSBC has been appointed to oversee the flotation on the London Stock Exchange, which will take place at the end of this month.
888.com is keen to avoid the market concerns over US gaming laws, which hampered the £4.6bn June flotation of Partygaming. Financial Dynamics handled that brief (PRWeek, 4 February).
In a bid to assuage investors' concerns, Cassava has already said that 45 per cent of its registered users, reportedly numbering around 20 million, live outside America and are therefore unaffected by US gaming laws.
888.com's listing will be a huge windfall for Avi and Aharon Shaked, who own 70 per cent of the firm, and the Ben-Yitzhak family, which reportedly owns 23 per cent.
The Shaked brothers will sell up to 30 per cent of their stake in the flotation, reaping them about £160m in cash and leaving them with a £424m holding.