The Irish rider rode the 11-1-shot horse, trained by Henry de Bromhead, at the famous race at England’s Aintree Racecourse to a victory by six-and-a-half lengths.
Previously, the closest any woman had come to winning the Grand National was Katie Walsh’s third-place finish onboard Seabass in 2012.
De Bromhead also trained runner-up Balko Des Flos. Any Second Now was third, with Burrows Saint fourth.
The Grand National has been taking place at Aintree Racecourse, near Liverpool in England, since 1839.
Blackmore’s momentous achievement comes as part of her breakout season after being the leading rider at last month’s Cheltenham Festival.
And in the 173rd edition of the historic race, Blackmore — wearing the green and yellow colors of owner JP McManus — put on a racing masterclass.
She bided her time round the 30 fences and over more than four-and-a-quarter miles, claiming victory with a sprint over the final section.
“He was incredible and jumped beautifully and I was trying to wait for as long as I could. When we jumped the last and I asked him for a bit he was there … This is just unbelievable.”
Although there were no fans at the event, the moment was not lost on those involved in the race as they stood and clapped Blackmore when she returned to the winner’s enclosure.