The captain beat away competition from the likes of Petr Cech, Victor Valdes and Joe Hart to take the International Federation of Football History and Statistics award
The Spain international received 224 votes to win - 96 more than second-placed Buffon - and it is the fifth time that he has taken home the IFFHS award in his career.
The 31-year-old has responded on his Facebook page, thanking the Madrid fans for their support.
"I am very pleased with this award," he wrote on the social networking site.
"And once again, I want to dedicate it to all the fans.”
The Blancos captain hit the headlines at the tail-end of 2012 after Jose Mourinho opted to drop him for reserve shot-stopper Antonio Adan in the club’s 3-2 defeat by Malaga at La Rosaleda.
However, Casillas was able to beat away competition for the award from the likes of Chelsea’s Petr Cech, Barcelona’s Victor Valdes, Juventus’ Gianluigi Buffon, Bayern Munich’s Manuel Neuer and Manchester City’s Joe Hart.
Casillas had a stellar 2012, with the two highlights being the dismantling of Barcelona as La Liga champions and winning the Euros with la Roja.