Progress of thermal tumor therapies and their translation into clinical practice are limited by insufficient nanoparticle concentration to release therapeutic heating at the tumor site after systemic administration. Herein, the use of Janus magneto‐plasmonic nanoparticles, made of gold nanostars and iron oxide nanospheres, as efficient therapeutic nanoheaters whose on‐site delivery can be improved by magnetic targeting, is proposed. Single and combined magneto‐ and photo‐thermal heating properties of Janus nanoparticles render them as compelling heating elements, depending on the nanoparticle dose, magnetic lobe size, and milieu conditions. In cancer cells, a much more effective effect is observed for photothermia compared to magnetic hyperthermia, while combination of the two modalities into a magneto‐photothermal treatment results in a synergistic cytotoxic effect in vitro. The high potential of the Janus nanoparticles for magnetic guiding confirms them to be excellent nanostructures for in vivo magnetically enhanced photothermal therapy, leading to efficient tumor growth inhibition. Double‐faced (Janus) gold‐iron oxide nanoparticles combine magnetic and plasmonic features as smart multifunctional platforms for theranostics nanomedicine. Herein, they are proved as efficient therapeutic nanoheaters under both magnetic hyperthermia (MHT) and photothermia (PTT) procedures. Thanks to the magnetic core, PTT can be improved on‐site upon systemic administration and magnetic guiding, leading to tumor growth inhibition.