"It just shows with opportunity and support and determination, anything can happen," he added.
As usual, one of the dances in the grand finale was chosen by the judges, one was their own favourite dance from the series, and the other was a show dance.
The judges gave advisory scores but the public made the final decision.
McCausland and Buswell performed routines including their waltz to You'll Never Walk Alone by Gerry and the Pacemakers in the grand final.
The pair also reprised their couple's choice routine to Instant Karma by John Lennon.
When they first performed it last month, it went viral on social media thanks to a "blackout moment", designed to imitate McCausland's experience with blindness.
They repeated the moment in the grand final, impressing the judges and getting them a score of 38.
"Chris, I am a mess because of you, and I said I would not cry in this final," said judge Motsi Mabuse, as she wiped away tears.
McCausland was registered blind after gradually losing his sight to retinitis pigmentosa in his 20s and 30s.
The winning duo faced stiff competition from the other remaining couples - JB Gill and Lauren Oakley, Tasha Ghouri and Aljaž Škorjanec, and Sarah Hadland and Vito Coppola.
Gill and Oakley were first to take to the dance floor.
The pair performed routines including a Show Dance to a Motown Medley and a Viennese Waltz to Let's Go Fly A Kite from Mary Poppins.
The latter received the first top marks of the night, with straight 10s awarded by the judges.
It came after the singer's original dance partner, Amy Dowden, was forced to pull out of the series last month due to a foot injury.
Next up, it was time for Ghouri and Škorjanec, who reprised their American Smooth routine to Someone You Loved by Lewis Capaldi.
They also performed a show dance to Sing, Sing, Sing by Benny Goodman.
Ghouri is Strictly's second deaf contestant, three years after Rose Ayling-Ellis won the contest.
There was also a poignant moment when her brother surprised her, having just landed back from Australia.
"Can't describe it," he said, as they hugged. "Follow your dreams. You're so special."
Finally, Hadland and Coppola performed routines including a Cha Cha to Like A Prayer by Madonna.
They also did an American Smooth, scoring them 39 out of 40 - despite Coppola suffering a wardrobe malfunction.
Gill and Ghouri topped the final leaderboard, with 119 points each - followed by Hadland with 118, and McCausland at 116.
But after weeks of tangos, salsas and foxtrots, it was McCausland and Buswell's night as they topped the public vote.
A charity has praised McCausland's win, saying it will "lead to many more disabled people being included in the biggest TV shows".
Steven Morris, who is deafblind and the campaigns officer for the disability charity Sense, said: "Chris's historic Strictly Come Dancing win goes to show that given opportunities and support, disabled people can break down barriers many wrongly don't think are possible."
He added: "This is an important moment for representation."
Other highlights on the night included a spectacular dance number, where the Strictly professionals were joined by Worth It singer Raye.
The entire line-up of 2024 also came back for one more routine.
There have been plenty of twists and turns in the show's 20th anniversary year.
Highlights included Bollywood music coming to the ballroom, when contestant Punam Krishan and her partner Gorka Márquez danced to Bole Chudiyan from 2001 hit film Kabhi Khushi Kabhie Gham.
It was the first time in the show's history that a competing couple have performed to a traditional Bollywood song.