Global warming necessitates the development of bio-based materials, with natural fibre composites offering a carbon-negative solution for large-volume applications such as civil engineering structures. However, their hygro-thermal durability, particularly moisture sensitivity, remains a challenge. This research investigated the moisture aging, fatigue, and creep behaviour of natural fibre composites, alongside strategies to enhance their long-term performance. Experimental studies involved cyclic moisture loading, immersion testing, and outdoor exposure, often combined with mechanical fatigue and creep tests conducted in controlled climate chambers. Results indicate that composite stiffness decreases with increasing humidity, with the extent of reduction (e.g., up to 40% in poorly bonded systems) highly dependent on the matrix and fibre-matrix adhesion. Fatigue behaviour of natural fibre composites was comparable to glass fibre systems, with stiffness tending to stabilize or even increase over fatigue cycles, a distinct characteristic. Creep studies revealed that the secondary creep rate is predictive of failure time, and time-temperature superposition enabled lifetime predictions, with estimates reaching 142 years under specific conditions. Good fibre-matrix adhesion consistently limited creep, with plasma treatments demonstrating reduced creep strain. Durability improvement strategies explored include using lignin-rich fibres like bamboo to reduce water uptake, applying enzymatic treatments to lower water absorption and diffusion, and utilising pre-swollen fibres during manufacturing to mitigate initial swelling-induced damage and improve mechanical property retention during cyclic moisture exposure. While immersion testing typically showed property degradation, cyclic moisture tests sometimes revealed an initial property decrease followed by an improvement, termed "hornification." Overall, enhancing fibre-matrix adhesion and employing pre-swollen fibres show significant promise for improving durability. Future work will investigate barrier coatings to further prevent component leaching and improve long-term performance.