Synthesizing metal-free, low-cost, and durable electrocatalysts that are active for the oxygen evolution reaction (OER) is essential for the development of commercial alkaline water electrolyzers. Herein, we develop a nanoconfined synthesis approach for the fabrication of a metal-free graphitic mesoporous carbon nitride (gMesoCN) electrocatalyst with a high surface area of 406 m2/g and high nitrogen content of 48%. This is achieved by a nanohard-templating approach through simple polymerization of guanidine hydrochloride (GndCl) as a single carbon-nitrogen source inside the organized mesopore channels of a mesoporous SBA15 silica nanotemplate. The produced material is characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM), which confirmed the formation of a well-ordered mesoporous carbon nitride, while analysis of the pore size distribution indicated the formation of uniformly sized pore channels of 4.56 nm. X-ray photoelectron spectroscopy (XPS) indicated that gMesoCN consisted of C and N. The metal-free gMesoCN material showed good electrocatalytic performance for the OER in alkaline medium, where a Tafel slope of 52.4 mV/dec indicated favorable OER kinetics. Significantly, the gMesoCN material demonstrates long-term durability with 98.4% retention of current density after 24 h. The reported gMesoCN material is inexpensive, environmentally friendly, and easy-to-synthesize with the potential for applicability in the field of electrocatalysis.