The development of visible-light-responsive photocatalysts for promoting solar-driven oxygen (O2) production from water splitting is a potentially attractive but still a challenging scheme. In the present work, a (111)-type layered perovskite oxynitride, Sr5Nb4O15−xNx, was synthesized via the nitridation treatment of the disk-like oxide precursor under the ammonia flow, which was fabricated using a flux method. The homogeneous dispersion of nitrogen (N) dopant in N-doped Sr5Nb4O15 was ascertained by energy-dispersive X-ray spectroscopy characterization, and the Sr5Nb4O15−xNx was found to be a direct semiconductor with a light absorption edge of approximately 640 nm. Density functional theory investigation implies that the hybridization between the outmost N 2p orbitals and O 2p orbitals upshifts the original valence band maximum of Sr5Nb4O15 and endows its visible-light-responsive characteristics. Loading with cobalt oxide (CoOx) as cocatalyst, the as-prepared Sr5Nb4O15−xNx exhibited an enhanced photocatalytic O2 evolution activity from water splitting under visible-light illumination (λ > 420 nm). Moreover, another homogeneous N-doped layered perovskite-type niobium (Nb)-based oxynitride, Ba5Nb4O15−xNx, was also developed and investigated for the visible-light-actuated O2 production, highlighting the versatility of the present approach for exploring novel visible-light-responsive photocatalysts.