Rowberry, who joined Lewis as partner from GCI Financial in March 2002, said New York-based Lewis Financial would be launched over the next three months.
'The main reason for doing this was the feedback we were getting from clients who wanted to consolidate their comms,' she added.
Although the agency handles corporate work, its experience of investor relations has been relatively limited, but Rowberry said the firm was in negotiations with existing clients to take on their IR.
Rowberry took up the role of head of comms at Scottish Telecom in 1997 and oversaw the company's flotation as Thus in 1999.
She joined GCI Financial in March 2001 as associate director before moving to Lewis one year later.
Former Stream International director of corporate comms and Lewis Boston general manager Steve Capoccia is also set to take a role at Lewis Financial.