The paper discusses the potential ingress and combined effect of moisture and temperature on pre-fatigued glass fibre-reinforced polymers standard test specimens. An experimental investigation was conducted to analyse the behaviour of glass fibre-reinforced polymers' in environmental conditions similar to that of tropical environments. The standard pre-fatigued glass fibre-reinforced polymers specimens were subjected to varying hygrothermal conditions: three different temperatures, i.e. natural bath, 45 °C and 55 °C to study the degradation in strength and related properties. Several macro-structural and micro-structural tests were conducted to determine the damage. The effect of these conditions on characteristics such as diffusivity, weight gain, resin volume fraction, conductivity and deterioration of ultimate tensile strength was determined. The maximum reduction in strength is found to be approximately 39% for the specimen exposed to 55 °C water bath for 60 days. This study shall be helpful in estimating the characteristics of glass fibre-reinforced polymers composites subjected to cyclic fatigue loads in the tropical conditions. © IMechE 2016.