Epoxy is the most prevalent thermosetting resin in the field of polymer composite materials. There has been a growing interest in the development of bio-based epoxy resins as a sustainable alternative to conventional petrochemical epoxy resins. Advances in this field in recent years have included the use of various renewable resources, such as vegetable oils, lignin, and sugars, as direct precursors to produce bio-based epoxy resins. In the meantime, bio-oils have been produced via the decomposition of biomass through thermochemical conversion and mainly being used as renewable liquid fuels. It is noteworthy that bio-oils can be used as a sustainable resource to produce epoxy resins. This review addresses research progress in producing bio-oil-based epoxy resins from thermochemical processing techniques including organic solvent liquefaction, fast pyrolysis, and hydrothermal liquefaction. The production of bio-oil from thermochemical processing and its use to inject sustainability into epoxy resins are discussed. Herein, we intend to provide an overall picture of current attempts in the research area of bio-oil-based epoxy resins, reveal their potential for sustainable epoxy resins, and stimulate research interests in green/renewable materials.