Organophosphate ester (OPE) flame retardants and plasticizers have replaced several legacy, banned brominated flame retardants. Bisphenol A bis(diphenyl phosphate) (BPADP) exemplifies a growing industry trend towards production of complex, high molecular weight, 'novel' OPEs. An assay method was optimized for quantification of BPADP biotransformation to target metabolites bisphenol-A (BPA) and diphenyl phosphate (DPHP) in an in vitro Wistar-Han rat liver microsomal assay. In silico modelling via OECD Toolbox v4.4.1 and Non-Target Analysis (NTA) via Q-E-Orbitrap HRMS/MS were applied to predict physico-chemical properties and identify additional non-targeted metabolites of BPADP. DPHP and BPA were predicted in silico and confirmed in vitro, with BPADP demonstrating slow in vitro microsomal metabolism. Additional Phase I oxidation metabolites & one Phase II GSH adduct were identified via NTA. These findings add to the understanding of BPADP stability and biotransformation, factors highly applicable to hazard assessment of the compound as an alternative to legacy flame retardants.