Natural fibre from plant-based reinforced polymer composites (NFRPCs) offers an attractive solution for various applications due to their cost-effectiveness, sustainability, and favourable properties. These materials provide high strength and stiffness while remaining lightweight, which is especially advantageous in weight-sensitive applications. However, their susceptibility to high flammability poses a significant challenge for applications requiring robust fire resistance. Consequently, researchers and engineers face the primary task of enhancing flame retardancy and thermal stability in NFRPCs. This paper provides a comprehensive review of the flammability and flame retardancy aspects of NFRPCs, delving into critical elements such as modification methods, the interfacial bond between natural fibres and the polymer matrix, fibre type, loading ratio, fibre orientation, polymer type, and composite structure. Understanding these factors is crucial for improving material fire resistance. The paper explores various flame-retardant strategies for NFRPCs, including additives, coatings, treatments, and nanomaterial hybridization. Detailed insights into mechanisms and characterization techniques related to thermal and flame retardancy are provided, covering aspects like thermal degradation, char formation, gas-phase reactions, fire testing methods, universally accepted standards, and specific flame-retardant requirements for NFRPCs in diverse applications such as automotive, aerospace, marine, and civil construction. The discussion on future directions emphasizes the development of innovative flame-retardant materials, improving composite design and fabrication improvements, and assessing fire performance and environmental impact.