Due to its high energy storage density at room temperature, silver niobate (AgNbO3) is one of the most promising lead-free dielectric perovskites for energy storage applications. In this work, reactive d.c. magnetron co-sputtering from Nb and Ag targets in Ar–O2 atmosphere at different substrate temperatures is employed to identify a process window for the synthesis of AgNbO3 thin films. Structural analysis by X-ray diffraction and Raman spectroscopy confirmed the formation of AgNbO3 at deposition temperatures of at least 550 °C or at post-annealing in ambient air at temperatures of at least 525 °C. Even though all deposited films contained a non-negligible amount of metallic Ag, an undesired inhomogeneity for the intended use of the films as antiferroelectric material in energy storage applications, the current work clearly shows the potential of reactive d.c. magnetron sputtering for the synthesis of lead-free crystalline perovskite thin films based on AgNbO3 and, hereby, opens pathways for future deposition process scalability.