Moisture damage and low-temperature cracking are common distresses experienced by road pavement. Different types of modifiers, such as fibers, can be used to improve the quality of asphalt pavements. In this paper, lignin and glass fiber were selected as additives to enhance the water- and low-temperature stability of the asphalt mixtures. The main objective of this study was to evaluate the composite effects of adding lignin fiber and glass fiber to a bituminous mix using experimental methods. The Marshall immersion, freeze–thaw splitting, and three-point bending tests were applied to evaluate the efficiency of lignin fiber (and/or) glass fiber modified asphalt mixes with regard to moisture damage and low temperature. Four kinds of asphalt mixtures, namely, the control asphalt mix (C), lignin fiber modified asphalt mix (L), glass fiber modified asphalt mix (G), and a composite of lignin fiber and glass fiber modified asphalt mix (LG) were evaluated. The experimental results showed that with the addition of 0.30% lignin fiber and 0.30% glass fiber the water stability, low-temperature stability, and quality of bituminous mix were improved significantly. With lignin fiber, the asphalt mixtures showed better resistance to thermal cracking, while glass fiber resulted in greater moisture susceptibility. The composite admixture was more effective than either lignin or glass fiber in modifying the asphalt performance. This clarifies the great beneficial effect of using the composite mixture in the asphalt mixtures industry.