Abstract Development of solid mixed oxide catalyst from waste biomass is a scarcely studied area. Thus, present protocol aims to prepare an environmentally friendly, efficient, renewable and recyclable heterogeneous base catalyst from Carica papaya stem. The chemical and structural properties of the catalyst were examined by Fourier-transform infrared spectroscopy (FTIR), X-ray diffractograms (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-ray spectrometry (EDX), Transmission Electron Microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis. The CO2-TPD and Hammett indicator test was conducted to determine the basicity of the prepared catalyst. The study revealed the presence of alkali and alkaline earth metals that provide the basic sites to facilitate transesterification reaction for biodiesel production and formation of benzylidenemalononitrile (BMN). The conversion of the waste cooking oil (WO) and Scenedesmus obliquus (SO) lipid to biodiesel was confirmed by the NMR and Gas chromatography Mass Spectroscopy (GC-MS) technique. Biodiesel conversions of 95.23% and 93.33% were achieved using 2 wt % catalyst loading under optimized reaction conditions for WO and SO respectively. Reusing the catalyst showed a slight drop in activity after 6 repeated uses. The reported catalyst has shown its potential as an alternative and cheaper green solid catalyst for biodiesel production and Knoevenagel reaction.