Herein, we report the synthesis and characterization of rGO-CdS heterostructure and their utilization as an efficient material for sensing and visible-light driven photocatalytic degradation applications. The heterostructure was synthesized by facile hydrothermal process and characterized by several techniques which exhibited intriguing compositional, morphological, structural, thermal, textural and photo-physical properties. The high resolution transmission electron microscopy (HRTEM) images of the prepared rGO-CdS heterostructure showed the successful deposition of CdS nanoparticles (CdS NPs) on the surface of reduced graphene oxide (rGO) sheets. The synthesized rGO-CdS heterostructure was employed as an outstanding fluorescent sensor for the selective and sensitive detection of heavy transition metal ion; Ag(I) and a synthetic food colorant; sunset yellow (SY). The detection limit of 12.35 pM and 7.89 pM was found to be for Ag(I) and SY, respectively. The prepared rGO/CdS heterostructure was also successfully applied for the photocatalytic degradation of fluoroquinoline antibiotic, levofloxacin (LVX), and food colorant SY under visible-light irradiation. The removal efficiency of 82.7% was obtained for LVX (10 mg/L) using rGO-CdS heterostructure in 60 min under visible-light irradiation. The synthesized heterostructure displayed enhanced photocatalytic decomposition (82.7%) than pure CdS NPs (67.5%) under optimized reaction conditions (0.50 g/L photocatalyst amount, 10 mg/L LVX initial concentration and pH 9.0). Approximate 66% of SY was degraded in 270 min under visible-light using the prepared heterostructure. The scavenger study confirmed the pivotal role of e, 02-, "OH, and "OH in the photocatalytic decomposition process. The amended photocatalytic behaviour of the rGO-CdS heterostructure could be accredited to the enhanced visible light harvesting capability, effective charge separation and transportation of photo generated charge carriers across the heterojunctional interface. To the best of our knowledge, this is the First report till date on the utilization of rGO-CdS heterostructure for the fluorescence sensing of Ag(I) and SY as well as photocatalytic degradation of LVX and SY.