The news comes as the company confirmed it is to change its name by the end of the year in a bid to reinvent itself.
British Biotech, which had a number of drug failures during clinical trials in the mid-1990s, has recently suffered a depressed share-price, hitting an all-time low last month.
Gadd joins from Pfizer, where she was global head of anti-viral compounds.
Prior to Pfizer, Gadd - a PhD pharmacologist - worked as chief of European and UK regulatory groups at the then HMR, now part of Franco-German pharmaceutical group Aventis.
British Biotech researches and develops drugs to help fight diseases with limited treatment options.