The 14-1 shot, ridden by Derek Fox and trained by Lucinda Russell, charged clear to finish ahead of Cause Of Causes (16-1) and Saint Are (25-1).
It was an unexpected win for jockey Derek Fox, too. None of those victories compare to the $1.25 million Grand National.
The wait for Scotland's second Grand National hero has been nothing like so long as the wait for the first, but 1979 victor Rubstic remains the country's only Aintree hero.
In sunny conditions in Liverpool, 19 of the 40 horses finished the race, with Aintree reporting afterwards that all runners came back safely.
"I am so pleased for the team", Russell said. He's just such a courageous horse.
Fox thought he'd blown his chance of a debut ride in the race when he broke his left wrist and right collarbone in a fall at Carlisle on March 9. "I'm very much aware it's possible I'll be further back than most Grand National winners come from, but he came from a similar position in the Becher and at Warwick". "He's the gamest horse I've ever ridden and he galloped all the way to the line".
Trained by Lucinda Russell - the partner of former eight-time champion jockey Peter Scudamore - One for Arthur became only the second Scottish victor of the race.
She said: "It means everything". "He's improved every time". "The dream for most racehorse owners would be to win the Grand National and we are lucky we found a horse to do it".
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"Together [Peter and I] we have had good and bad times but the horses are all back in form now".
"He's a bit one-paced and can be slow into stride", said Fox. I can't believe it. It's been an absolutely unbelievable day.
One For Arthur is just the second Scottish victor of the Grand National, taking up the mantle from Rubistic in 1979.
"He's given us a fantastic journey". It's just incredible. I'm so proud of the horse.
"He's awesome and he got a great ride".
One For Arthur took the lead in the 4 1/2-mile (6,400-meter) race for the first time over the 30th and last fence, before holding off Cause of Causes in the long run to the post.
"It was amusing, but everything has just gone so smoothly including winning the race".
Jumping in the north is regularly - and correctly - portrayed as the poor relation to its cousins in the south.