Financial Dynamics has won a two-way pitch to secure the brief for Merrill Lynch and HSBC's joint on-line investment and banking venture, set to launch by Christmas.
The City PR consultancy was hired following a pitch against Edelman Public Relations Worldwide.
FD will work on a project brief to launch the service - which is yet to be named - in the UK. The service will be rolled out in Canada and Australia in the first quarter of next year, then globally, except the US.
Andrew Waterworth, a partner in FD's financial services practice, will lead the account, heading a team of five.
At Merrill Lynch HSBC, he will report to chief marketing officer Victor Dodig and Merrill Lynch media relations head, EMEA, Neal Jenkins.
Jenkins said: 'Financial Dynamics will be playing an important part in promoting the venture to the target retail audience - consisting of independent affluent investors who want to make their own investment decisions.'
'It's predominantly a name awareness campaign that will seek to drive consumer traffic to the site,' said Waterworth.
Initially, the remit will mainly include press and media relations.
Jenkins added that FD's brief will be reviewed after the launch with a view to permanently retaining the agency. FD is already retained by Merrill Lynch Investment Managers.
Merrill Lynch and HSBC announced the joint internet business, with a combined investment of pounds 700 million, in April.
The product - based on Merrill Lynch Direct, which is already up and running in the US - will offer customers the opportunity to invest in products including stocks, bonds, mutual funds and unit trusts.