Track-etched polymer membranes with crossed nanochannels have been revealed suitable as templates for the electrodeposition of interconnected magnetic nanofiber networks with controlled morphology, material composition and nano-architecture. Three-dimensional networks of nanowires, core-shell nanocables, nanotubes and multilayered nanowires have been successfully fabricated. The interconnected structure provides the mechanical stability and electrical connectivity to the self-supported three-dimensional nano-architectures, while the polycarbonate template provides flexibility to the system. In addition, the local removing of the cathode enables a two-probe design suitable for electric and thermoelectric measurements, with the electric current flow restricted along the nanofiber segments. The tunability of the magnetic, magneto-transport and thermoelectric properties of various three-dimensional interconnected magnetic nanofiber networks has been demonstrated. The unique architecture of the three-dimensional nanofiber network system has been found suitable for a wide range of applications such as three-dimensional magnetic sensoring, magnetic devices with controlled anisotropy and microwave absorption properties, light and planar flexible thermoelectric modules for active cooling of hotspots and spin-caloritronic devices.(FSA - Sciences de l'ingénieur) -- UCL, 202