Pt nanoparticles (NPs) are successfully synthesized via sonochemically assisted green synthesis by using Prosopis farcta fruit extract (P. farcta) as a reducing agent and stabilizer. The synthesized Pt NPs are fully characterized to confirm the morphology, structure, colloidal stability, and biocompatibility. These Pt NPs exhibit excellent physicochemical properties and colloidal stability in aqueous solution with a zeta potential value of −38.9 mV. The high stability and biocompatibility of the Pt NPs can be attributed to the organic compounds contained in the P. farcta extract. The organic compound-coated Pt NPs are identified. The high energy produced by ultrasound irradiation facilitates a covalent interaction between the P. farcta extract and the Pt NPs despite the short duration of synthesis. Special attention has been given to explain the underlying complex processes that describe the reaction mechanism of Pt NPs synthesized by P. farcta under sonication. Results showed that the cell viability of the synthesized Pt NPs is unaffected (nontoxic) at relatively high concentrations (100 μg/ml), thereby making it a promising method for synthesizing Pt NPs that are relevant for medical applications.