Microwave-assisted catalytic degradation technology, owing to its efficiency and controllability, has emerged as a pivotal research area for treating organic pollutants in water. In this study, we innovatively synthesized a Co-Ni@kelp-derived carbon composite (Co-Ni@KC) using kelp as a green carbon source and Prussian blue analogs (CoNi-PBA). Under 800 W microwave irradiation, Co-Ni@KC-3 achieved degradation efficiencies of 99.52%, 99.74%, 94.67%, and 99.69% for methyl orange, methylene blue, crystal violet, and rhodamine B, respectively, at 240 mg/L within 4 minutes, demonstrating excellent cycling stability. The degradation mechanism is attributed to the synergy between thermal and non-thermal effects. By utilizing marine biomass to construct high-performance catalysts, this study addresses the limitations of traditional catalysts, such as high cost and low efficiency, offering an economical and eco-friendly solution for dye wastewater treatment while opening new avenues for the high-value utilization of marine biomass resources.