In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field. Display omitted •The integration of AD and HTL offers a complementary approach to waste treatment.•Our review examines both sequencing approaches: HTL followed by AD, and vice versa.•Key parameters and pretreatments were assessed to enhance overall energy recovery.•Integrating AD and HTL aligns with the circular bioeconomy for waste valorization.•Innovative methods for toxicity reduction in the HTL-AD systems were reviewed.