Barca had to weather a first-half storm in which Lyonnes had a goal ruled out for offside after a VAR review and the few chances that fell to Pajor went unpunished, but she turned on the style in the second period on Saturday as her side won at a canter.
Lindsey Heaps had the ball in the net after 14 minutes when Cata Coll spilled Wendie Renard's header from a free kick, but the Lyonnes goal was chalked off for offside following a VAR review.
The French team, the competition's most successful club with eight titles, struggled to get shots on target and paid for it after the break.
In the 55th minute, Patri Guijarro won the ball deep in her own half and surged forward before picking out Pajor to her right, who finished clinically from a tight angle.
Pajor added her second 14 minutes later as the Lyon defence switched off and left her alone in front of goal. The 29-year-old Polish goal-poacher blasted a pass from Esmee Brugts into the net from close range.
Paralluelo put the game beyond doubt by blasting a superb third from distance in the 90th minute before adding another on the break three minutes later to cap off a brilliant second-half display from the Spaniards.
The victory was an emotional one for Barcelona winger Caroline Graham Hansen, who grew up a few hundred metres from the Ullevaal Stadium where the final was played.
"There's been a lot going on all season, so to win at home and close out everything we've been going through, it's amazing, it's extra-special to win at home in front of so many fans from Barcelona," Graham Hansen said.
"This is my home ground, I grew up here, I know every metre of this grass, so it's very special and I can't wait to bring the team out and party tonight."
