The 14-year-old impressed the public with his 'Singing In The Rain' routine, which had won him a place in the final earlier in the week.
Sampson will now perform in front of Prince Charles at the Royal Variety Show. He will also receive a cash prize of £100,000.
After the result was announced, George said: "I'm speechless - wow. Just thanks so much. You have changed my life."
George had previously auditioned for the first series of the talent show, but did not make it to the semi-final stage. Returning for a second attempt this year, he told the judges he was "bigger and better".
Simon Cowell told the teen last night: "You are the dancing version of Rocky, young man. You battled your way to the top. Congratulations."
Dance duo Signature were the runners-up in the competition, while 13-year-old opera singer Andrew Johnston finished in third place.
Winner George had previously vowed to pay off his mother's mortgage with the prize money.