Brussels-based start-up Blueprint Partners has been unveiled a year after Harrison left GPC as part of a global boardroom shake-up.
Although refusing to name clients, Harrison claims that she has 'half a dozen' already on board, covering the chemical, pharmaceutical and advertising sectors.
Around half her clients are understood to have once been on GPC's books.
Also, three of her seven-strong consultancy team are ex-GPC.
These are former GPC vice-president Louise Harvey, and consultants Ilana Bet-El and Sue Couldery.
The team also includes Fiona Martin, formerly a journalist at The Financial Times.
Harrison's departure from GPC came after 12 years with the firm, a stint which included the setting up of its Brussels office.