This study investigates the influence of multi-walled carbon nanotube (MWCNT) reinforcement on the tensile properties of epoxy-based and glass/epoxy composite materials. Tensile stress-strain analysis reveals that neat epoxy exhibits the lowest strength and elongation, while the inclusion of MWCNT significantly enhances tensile strength and strain by up to 31.63% and 29.02%, respectively, for different nanocomposite types. Improved performance is attributed to better dispersion and interfacial bonding achieved with functionalized MWCNTs. For glass/epoxy composites, functionalized MWCNTs enhance tensile strength, strain, and chord modulus by up to 29.29%, 20.88%, and 6.55%, respectively. Failure analysis reveals broom-like fracture patterns and dominant fiber pull-out, with damage primarily localized due to fiber-matrix debonding and delamination. Functionalized MWCNTs delay fiber breakage, resulting in improved bonding and stiffness. Reliability of test results was analyzed using Weibull statistics, with shape factors indicating reduced randomness in functionalized composites. Experimental and theoretical data showed close agreement, confirming the enhanced mechanical performance and reliability of MWCNT-reinforced composites. These findings underscore the potential of functionalized MWCNTs to significantly improve the tensile properties and structural integrity of composite materials.