Burns, who was vice president and managing director at Bebo, leaves the social networking site after a year.
In her new role, where she will be responsible for sales across nine countries, including Denmark, France, Germany, Spain, Sweden, and the UK, Burns will report directly to AOL global advertising and strategy president Jeff Levick.
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."
Before joining Bebo in July 2008, Burns was 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.
Prior to that, Burns was director, UK, Ireland and Benelux at Google, which she joined in 2001 as its first employee outside the US.
Earlier in her career she held sales positions at Altavista and Doubleclick, as well as Ziff Davis and News International.
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."