The design of heterojunctions for efficient electrochemical energy storage and environmental remediation are promising for future energy and environment applications. In this study, a molybdenum disulfide-graphitic carbon nitride (MoS2-g-C3N4) heterojunction was designed by applying simple mechanochemistry, which can be scaled up for mass production. The physical-chemical and photophysical properties of the as-prepared MoS2-g-C3N4 heterojunction were analyzed using a range of characterization techniques. The supercapacitance performance was determined by electrochemical half-cell measurements, and visible light-induced photoelectrochemical and photocatalytic performance was studied using photocurrent and model organic pollutant degradation experiments. The resulting MoS2-g-C3N4 under the optimized experimental conditions showed significantly higher photocatalytic activity and photoelectrochemical performance under similar visible photoirradiation conditions compared to the bare materials. The resulting heterostructure electrode delivered a higher capacitance of 240.85 F/g than the bare material (48.77 F/g) with good capacitance retention. The superior performance was attributed mainly to the robust light harvesting ability, improved charge separation, high surface area, increased mass transfer, and capacitive and conductive behavior. The convenient and mass production of heterojunctions using a simple and cost-effective method will provide a good example for the efficient design of visible light active photocatalysts and capacitor electrode materials for environmental remediation and energy storage device applications.