The Wales winger sprinted from the halfway line into the penalty area five minutes from time at the Mestalla in Valencia before slipping the ball brilliantly between the legs of FC Barcelona goalkeeper Jose Manuel Pinto to seal a 2-1 victory.
After a season disrupted by a series of niggling injuries when many questioned his exorbitant price tag, it was the perfect way to reward Real's efforts in engineering his move from Premier League side Tottenham Hotspur F.C.
"It was a perfect night," Gareth Bale told reporters.
"It is great to win trophies and I am very happy to have won my first title with Real Madrid," added the 24-year-old.
"This victory was for the fans for all the support they have given us, the atmosphere was fantastic."
Real Madrid are in with a chance of winning a rare treble of La Liga, Champions League and King's Cup this season and Bale said he was confident the team were capable of winning at least one more trophy.
His goal showcased his physical prowess as he left Marc Bartra, who headed FC Barcelona's 68th-minute equaliser after Angel Di Maria had opened the scoring in the 11th, for dead before homing in on goal.
"I had to run, Bartra pushed me and tried to block me but he couldn't," Gareth Bale said.
"I had to get around him. It was great to score the goal against FC Barcelona but better to win the match and the Cup."