Efficient solar energy harvesting through selective absorber coatings is critical for advancing sustainable thermal applications, such as domestic hot water production and water purification. Enhancing photo-thermal conversion while maintaining durability and ease of fabrication remains a challenge. To address this, a composite selective coating was developed by decorating a heat-resistant paint with aluminium and nickel particles, applied via air-spraying on the base paint layer. The coatings were characterized structurally, morphologically, and compositionally using optical microscopy, field-emission electron microscopy, UV-Vis spectroscopy, energy dispersive X-ray analysis, and elemental mapping. Photo-thermal conversion performance was evaluated by measuring solar absorbance and the maximum substrate temperature under solar irradiation using a flat-plate collector setup. The study correlates the photo-thermal conversion with the coatings’ structural and compositional features. Notably, the coating decorated with nickel particles achieved a maximum solar absorbance of 96.07%, enabling substrate temperatures exceeding the boiling point of water without the need for antireflection coatings. The fabrication method and superior photo-thermal properties position this composite coating as a promising candidate for domestic hot water generation and water purification applications, outperforming conventional selective coatings regardless of collector geometry.