Although it was Real who opened the scoring through the clinical Ronaldo, the first half belonged to Juventus and, specifically, Mario Mandzukic, whose stunning overhead strike leveled the match for the Italians.
But treble-chasing Juve’s hopes were killed off after the break as Real rose to the occasion to complete their first league and cup double in 59 years.
Casemiro’s deflected long-range strike put the La Liga champions ahead once again, while Ronaldo and substitute Marco Asensio made sure of the victory.
The match was being played amid heightened security following the Manchester terrorist attack which killed 22 people and injured more just under a fortnight ago.
Two-thousand police officers, including 200 armed officers, patrolled the streets of Cardiff on matchday as South Wales Police carried out what they had described as the “biggest single sporting security operation in the UK.”
Major roads in the city center had been shut since midnight and would not open until 03:30 BST Sunday, while fans zones had been sectioned off with barriers, and water travel along the River Taff was banned.
The stadium’s roof was also closed — to prevent the possibility of a drone strike — making it the first Champions League match to effectively be played indoors.
However, such visible security precautions did not dampen the mood.
The Welsh capital’s streets were a river of humanity throughout the day as up to 170,000 people — almost half the city’s population — helped create an astonishing atmosphere.
Street merchants selling memorabilia had sold out of scarves six hours before kick-off as traders enjoyed a bumper day like no other in a city which is accustomed to hosting grand sporting occasions.
Cardiff was the host city for the 1999 Rugby World Cup and matches were held at the national stadium during the 2015 Rugby World Cup.
But as South Wales Police assistant chief commissioner Richard Lewis told CNN before the match, this was an occasion of a “different magnitude”.
Brilliant atmosphere, brilliant goals
It was a contest billed as attack versus defense. Real — who have scored in every game this season — had to crack miserly Juventus, whose defence had conceded just three goals in their 12 Champions League games to this final.
What evolved, however, was a wonderfully inventive game, adorned by sublime first-half strikes.
The Italians started brilliantly, justifying Real manager Zinedine Zidane’s warnings that his former side was the complete outfit.
Twice former Real striker Gonzalo Higuain tested goalkeeper Keylor Navas in the opening five minutes.
But despite the treble-chasers’ dominance, it was Real who took the lead. With his first strike on goal, the ruthless Ronaldo found the bottom-left corner to score his 104th goal in the competition.
Juventus responded quickly with Mandzukic scoring one of the memorable European Cup goals.
Eighteen yards from goal, the Croat found the top-right corner with a breathtaking kick, setting off roars which were loud enough to uproot trees.
But the second half belonged to Real. They controlled the match and struck twice in quick succession to kill off Juventus’ hopes.
With 30 minutes remaining Casemiro’s long-range strike deflected off former Real’s Sami Khedira to wrong-foot Gianluigi Buffon in the Juve goal and Ronaldo provided the knockout blow, guiding home Luka Modric’s cross from an acute angle.
A comeback was made even more unlikely when substitute Juan Cuadrado was sent off for a second bookable offense just 18 minutes after entering the field.
In his 18 months are Real manager, Zidane has now won the Champions League twice and the Spanish league title.
Juventus, meanwhile, suffered again on football’s grandest stage. Having already won a record sixth consecutive Serie A title and the Italian Cup, they were bidding for the treble but lost for the seventh time in a European Cup final.
For 39-year-old Gianluigi Buffon, who will retire after the 2018 World Cup, it was likely his last chance to win European club football’s premier prize.
But the brilliant goalkeeper, who would have become the competition’s oldest winner had his team won, could do little about Real’s goals.