The La Liga leaders needed extra time, to beat hosts Kashima Antlers 4-2 in the final.
Karim Benzema opened scoring in the game against the J.League title winners, before Antlers went ahead through Gaku Shibasaki’s brace.
Ronaldo levelled from the spot on the hour mark, before adding two more to break the hosts’ resistance and win the trophy for Madrid. It is the second time in three years the Spanish giants will be winning the Club World Cup.
It is also the third trophy manager Zinedine Zidane is celebrating, after the Champions League and Super Cup.
The Portugal captain became the first player to score a hat-trick in the final of the competition and helped the La Liga club extend their record-breaking unbeaten run to 37 matches.
Ronaldo himself has made history time and again over the last 12 months.
On Sunday, the 31-year-old became the first player to win the Champions League, European Championship, Club World Cup and the Ballon d’Or in the same year.
The forward scored 16 goals in 12 Champions League matches, as Madrid won an 11th European crown. In the summer, he captained his country to their final major trophy in Euro 2016 staged in France.
He was rewarded for his brilliant performances with the Ballon d’Or – for the fourth time in his career.