<p>Nanotechnology has served enormously to preserve the environment in terms of detection and remediation of pollutants. Owing to multifunctional applications of noble metal nanoparticles, we have first time reported the <i>Carissa macrocarpa</i> fruit extract based greenly synthesized gold nanoparticles (CMFE@AuNPs) for cost effective sensitive sensing of Pb²⁺ ions, photodegradation of hazardous azo dyes and bactericidal applications. Phyto functionalized CMFE@AuNPs were synthesized by one step approach under sunlight and characterized by UV–Vis, FTIR, XRD, HR-TEM, EDX, DLS, and ZP analysis. Optimized ellipsoid-shaped CMFE@AuNPs having average crystallite size of 31.5&#xa0;nm have shown sensitive and selective detection potential to detect Pb²⁺ ions in spiked water with an LOD of 117&#xa0;nm. The effect of temperature, pH, and interfering ions showed the minimum effect on the detection of Pb²⁺ ions for real-time applications. CMFE@AuNPs have also shown remarkable photocatalytic potential by degradation of MB (83.1%) and MO (72.7%) under sunlight with rate constant values of 1.2 × 10^–2&#xa0;min⁻¹ and 0.87 × 10^–2&#xa0;min⁻¹ for MB and MO, respectively. The effect of temperature, pH, catalyst dosage, and various water compositions was analyzed on the degradation process. Thermodynamic and kinetic studies showed the endothermic and non-spontaneous nature of the degradation process. Additionally, CMFE@AuNPs have also shown appreciable antioxidant activity with an <i>IC</i>_<i>50</i> value of 25.4 ± 1.1&#xa0;μg/mL accessed by DPPH scavenging assay and antibacterial applications by inhibiting the growth of gram-positive and gram-negative bacterial strains. Hence, it has been concluded that these CMFE@AuNPs can be used as portable Pb²⁺ sensors and water purification applications at a commercial scale.</p>