This study investigates the effect of tomato and grape pomace powders on the structural and rheological properties of carrot-based mousses, with complementary physicochemical and compositional analyses. The incorporation of tomato pomace (TEP) resulted in increased viscosity, adhesiveness, and cohesiveness, accompanied by a brighter and more color-stable appearance. In contrast, grape pomace (GPP) enhanced hardness and contributed to a more compact internal structure, while producing darker and less saturated color tones. Both pomace powders significantly affected the microstructure and elemental composition of the mousses. The tomato pomace was associated with a higher relative abundance of potassium and magnesium, whereas the grape pomace increased the relative levels of nitrogen, phosphorus, calcium, and iron. Increasing pomace concentrations led to a decrease in pH, particularly in the TEP_3.0 and GPP_3.0 variants, indicating an acidifying effect of the added plant materials. The results demonstrate that fruit and vegetable pomace powders can effectively modulate the structural, rheological, and compositional characteristics of plant-based mousses. These by-products represent functional ingredients that support the valorization of food processing waste and offer technological potential for the formulation of fiber- and polyphenol-enriched semi-solid food products within a circular economy framework.