Ananas comosus leaves were converted to a porous graphitized carbon (GPLC) material via a high-temperature pyrolysis method by employing iron salt as a catalyst. A cobalt molybdate (CoMoO₄)-and-GPLC composite (CoMoO₄/GPLC) was then prepared by engineering CoMoO₄ nanorods in situ, grown on GPLC. N₂ adsorption–desorption isothermal curves and a pore size distribution curve verify that the proposed composite possesses a porous structure and a large specific surface area, which are favorable for charge and reactant transport and the rapid escape of O₂ bubbles. Consequently, the as-synthesized CoMoO₄/GPLC shows low overpotentials of 289 mV and 399 mV to afford the current densities of 10 mA cm⁻² and 100 mA cm⁻² towards the oxygen evolution reaction (OER), which is superior to many CoMoO₄-based catalysts in previous studies. In addition, the decrease in current density is particularly small, with a reduction rate of 3.2% after a continuous OER procedure for 30 h, indicating its good stability. The excellent performance of the CoMoO₄/GPLC composite proves that the GPLC carrier can obviously impel the catalytic activity of CoMoO₄ by improving electrical conductivity, enhancing mass transport and exposing more active sites of the composite. This work provides an effective strategy for the efficient conversion of waste ananas comosus leaves to a biomass-derived-carbon-supported Co-Mo-based OER electrocatalyst with good performance, which may represent a potential approach to the development of new catalysts for OER, as well as the treatment of waste biomass.