HSBC CIBM global head of corporate comms Pierre Goad said the division had rebuilt its equities business to cope with increasing competition from other universal institutions and specialist investment banks.
He added: 'Clients' needs in equities trading are changing, margins have been shrinking and a lot of clients are no longer interested in the me-too research the rest of the industry is publishing.
'We are adding a lot more capacity, in a very competitive industry, in electronic trading and equity derivatives to give us a more sophisticated range of product.
'Donal's job will be communicating this to clients, the press and staff in other areas of the division.'
HSBC CIBM works for corporations, institutional investors, pension and hedge funds, governments and their agencies.
McCarthy, who reports to Goad, is the last of a dozen new hires to HSBC CIBM's London corporate comms team over the past year.
The division decided to manage its corporate comms globally two years ago and since then has hired 35 new staff to its 65-member global team.
They are split between New York, Hong Kong and the Philippines.