Ten-year-old Ruby Dailly plays the red-haired Ava, whose diminutive friend, Edgar, the excitable dragon, accidentally ruins a village's winter festivities before eventually redeeming himself.
The Glasgow youngster said she enjoyed her experience working with a cast of more than 100 people on the hotly-anticipated ad.
She said: "It's been nice to work with everyone behind the scenes. It was fun."
The advert follows Edgar as his excitement about festivities in his village sees him accidentally melting the ice-rink, reducing a snowman to a puddle and setting fire to a Christmas tree as his anxious friend Ava looks on.
Edgar finally shuts himself away in despair, but Ava encourages him to rejoin the village with the gift of a Christmas pudding, which allows him to put his fire to perfect use.
Ruby added: "He's a friendly dragon because he's pals with me. She keeps on being friends with the dragon, even though he sets everything on fire.
"He can't help setting things on fire when he's excited. He doesn't mean to so he gets sad whenever I'm mad at him."
Ruby's father, Graham, took to social media earlier this year to express his pride over his daughter passing the audition for the role.
Being careful not to reveal too many details, he wrote: "She absolutely smashed it and now we are off on our jollies to film a very high profile advert.
"It's all a bit hush hush in this industry with having to sign a privacy waiver etc. But what I will say is, I'm super proud of the wee rubstar and it's a massive move for her trying to break into the acting world."
John Lewis customer director Craig Inglis said: “I’m delighted our two brands have come together for this year’s Christmas campaign.
“It started from a spark of an idea – a little dragon’s excitement about Christmas – and became the story of how someone goes the extra mile for their best friend to give just the right gift.
“It’s a funny, heart-warming story that will resonate with our customers as they seek out the perfect gifts for their loved ones this Christmas.”
John Lewis’s ad follows big-budget campaigns from retailers including Argos, Asda, Amazon, Ikea and Sainsbury’s.
The Bear And The Hare advert run by John Lewis in 2013 remains amongst their most popular creations, set against Lily Allen’s cover of Keane’s Somewhere Only We Know.