Opuntia monacantha mucilage was investigated for its physicochemical characteristics and functional properties. The mucilage extraction yield was 12% (DW) and it consisted of 80.12% carbohydrates, 15.14% ashes, 3.55% proteins, and 1.19% lipids. Monosaccharide profiling demonstrated a predominantly presence of galactose, glucuronic acid, and arabinose. Viscosimetric measurements gave an intrinsic viscosity of 9.02 dL/g and a molar mass of 1.12 × 106 g/mol. Reconstituted mucilage solution (1% w/v) had a mean particle diameter (D4,3) of 648 nm and solubility above 85%. Its emulsifying capacity improved with the increment of mucilage solution in the emulsion; likewise, it provided high emulsion stability through different ratios of oil to polysaccharide solution. It displayed good foaming capacity, although its foam stability progressively reduced over time. In addition, its blending with ovalbumin resulted in a foaming capacity enhancement and in a markedly greater foam stability compared to ovalbumin alone. The rheological studies indicated the mucilage solutions exhibited shear-thinning behavior at concentrations between 1 and 10% and fairly stable viscous properties in the temperature range of 5–80 °C. These outcomes support that O. monacantha mucilage may find potentially useful applications in food systems, particularly as an emulsifying, foaming and thickening agent, or as a stabilizer.