Funnyman Chris Rock handed the director the honour for his film, which beat Shutter Island, Inglourious Basterds, Kick-Ass and 2012 for the title.
Accepting the award, Ritchie joked, "Thank you very much. We said no to the Oscar but we'll say yes to this because the public voted for it. We set out to make a comedy but we'll take it where we can get it."
Inglourious Basterds star Diane Kruger then introduced a clip of Sex and the City 2, which was hailed as the Most Anticipated Movie of the Summer.
A host of stars including Tom Cruise, Robert Pattinson, Daniel Radcliffe and Orlando Bloom are in attendance at the London ceremony.
Awards to come include Best Fantasy, Breakthrough Movie and Performance of the Year.