Remarkably, the nine-year-old horse, owned by Michael O'Leary, the chief executive of Europe's largest budget airline Ryanair, had never won over fences before and had suffered an injury-hampered career.
Yet he performed beautifully over the fearsome fences of the four-mile marathon, strongly coming through to storm past The Last Samuri and third-placed Vics Canvas, a 100-1 shot.
Mullins, the nephew of all-conquering trainer Willie Mullins and the latest success story in a famous Irish racing dynasty, could hardly believe his success on his National debut.
"Rule The World, what an aptly-named horse! It's unbelievable. I couldn't expect things to have gone any better," he told the BBC.
"To get the call to ride this horse was amazing. The fact that it is his first win over fences is more amazing than me winning on my first time around."
Rule The World ridden by David Mullins (R) jumps the last fence on his way to win the 5.15 Grand National Chase.
Image credit: Eurosport
For Rule The World, it was eighth time lucky after having finished second on seven occasions and connections suggested afterwards that, given his previous injuries, it might be the last race of his career.
The effervescent O'Leary, renowned for his outspoken comments as an airline boss, said he was virtually speechless.
His Gigginstown racing operation, which had delivered the Cheltenham Gold Cup winner Don Cossack three weeks earlier, could now celebrate victory in the two biggest and most lucrative races over the fences in Britain.
"I think I'm officially going to give up as an an owner now!" O'Leary joked on Channel 4. "David gave him a masterful ride."
He also praised a brilliant training performance by Morris, who was left emotional following a difficult year during which his son Christopher died in a freak accident in Argentina.
"It's like Disneyland. Someone is looking down on me," Morris, who also saddled Rogue Angel to victory in the Irish Grand National last month, told reporters. "I've got great friends who stood by me and helped.
"I'd have settled for third at the Elbow but he ran on like a train. He has injured his pelvis in two falls and before that he was one of the best horses I ever had."
The other co-favourite Many Clouds, looking to become the first horse since Red Rum to win the National in successive years, ran out of steam under Leighton Aspell, who was hoping to become the first jockey to win the race three years in a row.
The best news of all was that, although only 16 of the 40 starters finished the demanding course, all jockeys and horses returned safely after a difficult week at the Aintree festival which saw the death of four horses in the previous two days.