The longstanding problem of accessing F-theory on eight-dimensional manifolds of Spin(7) holonomy is addressed from an M-theory perspective. A novel version of the duality from M-theory to F-theory is proposed, in which M-theory on certain Spin(7) manifolds is dual to F-theory on the same geometries times an interval. The F-theory effective action is discussed by uplifting the M-theory effective action from three to four dimensions. The Type IIB weak-coupling limit of these setups is analyzed and their supersymmetry properties are discussed.