Swift revealed on Twitter that she wrote the song in 2008, but left it off the album at the time.
Swift sings: "Mr. perfect face. Mr. here to stay. Mr. look me in the eye and told me you would never go away.
"Hello, Mr. perfectly fine. How's your heart after breaking mine? Mr. always at the right place at the right time, baby. Hello, Mr. casually cruel. Mr. everything revolves around you. I've been Miss misery since your goodbye. And you're Mr. perfectly fine."
Swift last week shared the full tracklist for the new "Fearless." Keith Urban and Maren Morris make appearances on the new album, which features previously unreleased songs "Don't You," "Bye Bye Baby" and "You All Over Me."
Swift is re-recording previous albums after Scooter Braun's Big Machine Records purchased her masters.
"Fearless (Taylor's Version)" drops Friday.