The Alfie star hit the studio with rising musician Jack Savoretti, after the pair met during a night out in Soho’s star-studded Groucho Club.
The song is a romantic duet called Hate & Love.
A source said: “Jack met Sienna at the Groucho Club and she sang These Boots Are Made For Walkin’.
“She adores singing so jumped at the chance to sing with him when he asked her to.”
Miller has also recently joined the cast of romantic comedy A Case of You, which has just started filming in New York.
Listen to Miller’s track with Jack Savoretti: