The need for thermosets from renewable resources is continuously increasing to find eco-friendly alternatives to petroleum-derived materials. Products obtained from biomass have shown to play an important role in this challenge. Here, we present the structural characterization of new biobased thermosets made of humins, a byproduct of lignocellulosic biorefinery, and glycidylated phloroglucinol coming from the biomass phenolic fraction. By employing attenuated total reflection-Fourier transform infrared and NMR spectroscopies, we elucidated the connections between these two systems, contributing to clarify their molecular structures and their reactivities. We demonstrated that the resin curing takes place through ether bond formation between humin hydroxyl functions and phloroglucinol epoxides. Besides cross-linking, humins show a complex rearrangement of their furanic structure through different concomitant chemical pathways depending on the reaction conditions.