Thomson is currently managing director of AOL UK and executive vice-president of marketing for AOL Europe, having joined the company five years ago as marketing director.
In her new role, she will continue to oversee the management and marketing of the company's three UK brands -- AOL, CompuServe and Netscape Online -- with the expanded senior management team reporting to her.
Michael Lynton, CEO of AOL Europe, said, "Karen has built up a formidable business in the UK, and the successful campaign she led for pro-consumer reform of outmoded minute-by-minute metered internet call charges has put the UK, as a whole, at the forefront of the global internet revolution."
Thomson added, "When I joined AOL UK five years ago, I was excited to play a part in building a new medium. With more than 1m UK households turning to AOL for their daily communication, information and entertainment needs, we are beginning to realise our mission."
The key senior executive changes have seen Lori Friedman placed in the newly created role of chief operating officer and Anne Alexander appointed as group publishing director.
The restructuring has also seen three new director-level positions filled by Clare Lawrence as director of acquisition marketing; Sharon Lang, director of brand marketing; and Alex Boothroyd, director of customer operations.