Burns leaves her position at the AOL-owned social media company to take responsibility for expanding AOL's ad sales across Europe and scaling its Advertising.com third-party network.
She will report directly to the AOL global advertising and strategy president, Jeff Levick. No successor to Burns at Bebo has been announced, and she will continue to run Bebo's European operations while she settles into her new role.
Brendan Condon, the managing director of Platform-A's non-US business, whose responsibilities Burns will assume, will return to his native New York to take on a new role that is yet to be decided.
The AOL chief executive, Tim Armstrong, who took over in March, is conducting a review of the company's operations and is expected to present a strategy later this month.
Levick said: "Europe is key to realising our mission of being the largest global platform for online display advertising. Kate is the right person to build our European management sales team and lead this effort.
"Kate is a well-recognised and highly respected leader in Europe who has the talent, energy and determination to scale our European operations and deliver on this strategy. "
Burns said: "AOL has a solid foundation in Europe, with a strong web presence in many countries and a leading advertising network, and I’m looking forward to working with my colleagues and with AOL’s partners to build on this foundation.
Before joining Bebo in July 2008, Burns was the managing director of Dailymotion UK, where she was responsible for growing its audience, building an advertising sales operation and creating commercial partnerships with brands and ad agencies.
Burns has also been a director at Google, a company she joined in 2001 as its first employee outside the US. She has also held key sales positions at Altavista, Doubleclick and News International.