This paper describes the development of a novel high-performance thermoset based on epoxidized linseed oil and pure crystalline citric acid (CA). Fully bio-based polymer networks are generated and CA is shown to be a very efficient hardener for epoxidized plant oils. Comprehensive processing-structure-property relationships are established and optimum curing parameters are derived. The thermoset's polymer physical property profile (incl. high stiffness and strength) reveals its great potential to substitute petrochemical based resins.