In today’s scenario, the durability of the fiber reinforced polymer composites is one of the major concern for marine and construction sectors. In this context, the strength of glass-fiber reinforced polymer (GFRP) composite based pin joints was investigated under hygrothermal aging conditions with varying hole diameter. The composite pin joint specimens were made of neat epoxy with no nanofiller material and nanocomposite with nanoclay as nanofiller material. The nanoclay filler varying from 0 to 5 wt% was added into the epoxy, and it was found that at 3 wt% of nanoclay filler, the performance of the composite specimens was maximum. Thereafter, effect of hole diameter in GFRP composite pin joints was investigated for maximum bearing capacity, with optimized specimens further exposed to the hygrothermal aging. Hygrothermal aging of neat and 3 wt% nanoclay configuration specimens was conducted in distilled water (aging medium) at different temperatures, that is, 25°C, 45°C, 65°C and for different durations, that is, 15, 30, 45, and 60 days. It was found that the strength of composites decreases with an increase in aging temperature and duration. Nanoclay modified GFRP composite specimens showed better resistance to water absorption rate and had better strength retention ability than GFRP neat epoxy composite specimens.