No, Florence + The Machine is not a goth band, because they play Art Pop, Indie Rock, Folk, while goth music consists of Gothic Rock and its derived genres, like Deathrock, Darkwave, Ethereal Wave, and Coldwave.

If you want to dive into the goth music scene, some of the bands that might appeal to you if you enjoy Florence + The Machine are Dead Can Dance, Faith and The Muse, and Mors Syphilitica.