I Knew It, I Knew You was written and produced with longtime collaborator Jack Antonoff and will be released globally on June 5 across all major streaming and download platforms.
The single will also appear on the official Toy Story 5 soundtrack when it arrives on June 19.
Swift has also launched three exclusive CD editions through her official website, each featuring a different version of the song - the film version, an acoustic take, and a piano rendition.
Swift's new track draws directly from Jessie's storyline in the film, tapping into the cowgirl's emotional highs and lows.
The project sees the pop superstar leaning back into the country textures that shaped her early career, while still weaving in the pop sensibilities and narrative detail she's known for.
Jessie, who first galloped into the franchise in Toy Story 2, struck an immediate chord with Swift when she watched early scenes from the new instalment, prompting her to dive straight into writing.
Announcing the news on Instagram, she wrote: "It's a Toy Story. You knew it! My new original song 'I Knew It, I Knew You' for Disney and @pixar's @toystory 5 will be yours on June 5th ... I've always dreamed of getting to write for these characters who I've adored since I was a 5‑year‑old kid watching the first Toy Story movie ... I wrote this song as soon as I got home from the screening. Sometimes you just know, right?"
Director and screenwriter Andrew Stanton said Swift's instinctive understanding of Jessie's emotional state made the collaboration feel "meant to be".
He said Swift's song felt so naturally tied to the film that it was "like a long‑lost family member" returning to the franchise.
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