The thesis regards the extraordinary power of Sappho in the 1860s as resulting in a form of “Sapphic Possession” which laid hold on Swinburne, shaped his verse, produced a provocative new poetics, and which accounted for a critical reception of his work that was both hostile and enthralled. Using biographical material and Freudian psychology, I show how Swinburne became attracted to Sappho and came to rely on her as a substitute mistress and particular kind of muse, and I demonstrate the pre-eminence of the Sapphic presence in Poems and Ballads: 1, as a dominant female muse who exacts peculiar sacrifices from the poet of subjection, necrophilia, and even a form of “death” in the loss of his own personality; as a result, he is finally reduced to acting as the muse’s mouthpiece, a state akin to that of Pythia or Sibyl. Verse written under such duress instigates a new poetics where the demands and constructs of the muse produce a sublime composed of aberrance, fracture and the darkness of myth. To explicate this argument I read Poems and Ballads: 1 through carnival, a form of Bacchanal or Sapphic Komos which has the effect of blurring the boundaries between life and lyric, and which demands a joyous and reciprocal response from its readers, in which they must acknowledge their own attraction to the Sapphic sublime.