Due to their outstanding properties, fiber-reinforced polymer (FRP) composites are exceptional alternatives to conventional materials in numerous manufacturing applications. The effective joining of traditional materials with FRP composites is crucial for practical applications, necessitating detailed studies on joint performance under adverse environmental conditions. This study investigates the joining of aluminum plates and Kevlar fiber-reinforced polymer (KFRP) composites using bolted, bonded, and hybrid (bolted/bonded) joints. The joints were aged for one month at room temperature in normal water and seawater. After aging, the tensile strength of the joints was tested using a Universal Testing Machine (Instron 3382) at a constant crosshead speed of 1 mm/min. The results showed that tensile strength generally declined due to aging, with hybrid joints exhibiting superior strength to bolted or bonded joints. Interestingly, bolted joint strength increased with water aging but decreased with seawater aging, while bonded joint strength rose with seawater aging and declined with normal water aging. The tensile strength of seawater-aged hybrid joints was 4.7 kN compared to 5.8 kN for unaged joints. Post-failure analysis using Scanning Electron Microscopy revealed that the joints failed due to debonding, fiber pull-out, and fiber failure in the KFRP component. The hybrid joint specimens demonstrated superior mechanical performance under all environmental conditions. This study underscores the enhanced durability and mechanical integrity of hybrid joints in FRP composites, particularly under challenging environmental conditions, highlighting their potential for demanding applications.