Nanowire based magnetic spin valves utilizing a core-shell device architecture about free-standing Ni nanowires have been fabricated and characterized. Devices containing sequential shell layers of CoO(10 nm)-Co(5 nm)-Cu(5 nm)-Co(5 nm) deposited through sputter deposition around the chemical-vapor-deposited Ni core nanowires exhibit a giant magnetoresistance effect of ~9%, which matches that of the corresponding planar thin film multilayer. The Ni nanowires which serve as the device platforms are obtained in diameters ranging from 100 nm through 300 nm and typical heights of 20 micrometers or greater. Since the nanowires are oriented vertically upon Si/SiO2 growth substrates they allow the creation of core-shell spin valve devices with an orientation, aspect ratio, and distribution difficult to achieve with conventional thin film methodologies. The demonstrated, fully-functional, nanowire-based spin valve establishes the viability of magnetic multi-layer device structures in the core-shell implementation. Devices of this nature have potential in various applications including high-acuity magnetic field sensing.