The 29-year-old won gold in the individual and team events at London 2012 on-board the Dutch gelding Valegro.
She also collected freestyle and special titles at world and European level and won at the dressage World Cup finals in Lyon in April.
Dujardin is the third horsewoman to win the main award after Pippa Funnell and Zara Phillips.
She told Sky Sports: "I have an incredible relationship with Valegro, after working with him for eight years. He is like my dance partner and he should be receiving the award with me but he is at home in his stable."
"My next big competition is the World Cup final in Las Vegas next year and then the Europeans and the Olympics."
Photo: Charlotte Dujardin and Valegro at the WEG - Cecile vom Herzen for Equnews.fr