Flax Fiber Reinforced Polymer (FFRP) composites have gained attention for their environmentally sustainable qualities and mechanical performance, making them promising candidates for the construction sector. This research examines the dynamic mechanical properties of thermoplastic flax fibre-reinforced polymer (FFRP) composites using a Dynamic Mechanical Analysis (DMA) device. The study initially focuses on the influence of temperature on the material’s viscoelastic behaviour, essential for applications where materials are exposed to fluctuating environmental conditions. The material under investigation consists of flax fibres embedded in an Elium® thermoplastic resin matrix, selected for its recyclability and processing versatility. The composite laminates were manufactured using the Liquid Resin Infusion (LRI) technique, which ensures good fibre wetting and consistent laminate quality. This combination of natural reinforcement and thermoplastic matrix provides an environmentally friendly alternative for structural applications requiring thermal and mechanical performance. Additionally, frequency sweep tests are performed to assess the composite’s response to different frequencies. Data are further analysed using the Time-Temperature Superposition Principle (TTSP) to estimate long-term performance. The results indicate that the inclusion of flax fibres improves dynamic mechanical properties of the composite material. These findings provide valuable insights into the resilience and adaptability of FFRP composites, highlighting their potential for applications requiring durability and flexibility across varying temperatures and stress conditions.