Unsaturated furan-based ester (UES) was prepared by green electrosynthesis using a single-cell setup and inexpensive graphite electrodes. The UES was validated as a reactive diluent for a bio-based acrylated rapeseed oil (ARO). UV-light photopolymerization of the bio-based resin was initiated using a diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide (TPO) radical photoinitiator. The addition of 20 wt% UES to ARO dropped the resin viscosity by 1.6-fold. Incorporating 5 wt% UES into the ARO resin increased crosslinking density νe from 1.07 to 1.65 mol/m3. Fourier-transform infrared spectroscopy (FT-IR) spectra revealed that ARO has been grafted with UES. The UES functional moieties promote the formation of soft mobile dangling chain end segments in the developed macromolecular network. UV-cured thermoset polymer reveals distinct morphologies in SEM micrographs, indicating notable structural changes with the addition of UES. A total of 5 wt% UES increased tensile strength from 0.49 to 0.55 MPa and storage modulus from 7.9 to 12.0 MPa at room temperature (22 ± 1 °C). The biodegradability in composting conditions was investigated, and up to 28% of the initial mass was lost after 60 days. UES was shown as to be efficient reactive diluent that can successfully replace fossil-based acrylate monomers in vegetable oil-based thermoset polymer synthesis.