Sir Elton said he had seen Delevingne at Glastonbury music festival over the summer, where the pair had discussed how they would love to work together “if the right idea came up”.
“She’s hilarious to spend time with, we both have quite a self-deprecating sense of humour,” Sir Elton said.
When the idea of Delevingne playing him in the original music video came along, the pop star said it was “the perfect opportunity”.
“Thank God Cara thought the same, because it came out great.”
Delevingne, 32, said Sir Elton had “always been an idol of mine”.
“To say his music has had a deeply profound effect on me is an understatement.
“I hope that Elton may one day return the favour and agree to play me in my not yet developed, written, pitched or funded biopic. Fingers crossed.”
Step Into Christmas reached number 24 in the UK top 40 on its release in November 1973, and the top of the Billboard Christmas Singles chart in the US.
The song is currently number 15 in the UK singles chart.