This study aimed to analyze the effects of adding different peanut protein fractions before and after Lactobacillus pentosus fermentation on the water-holding capacity, cooking loss rate, texture, gel strength, rheological properties, chromaticity, and microstructure of heat-induced chicken breast meat gels. The goal was to investigate the impact of peanut protein fractions on the quality of chicken sausage gels and support the healthy development of China’s National Double Protein Engineering. The results demonstrated that the addition of peanut protein isolate (PPI), arachin, and conarachin, either before or after fermentation, significantly enhanced the water-holding capacity, gel strength, and gel hardness of chicken sausages. Among these, L. pentosus fermentation had the most pronounced effect on enhancing the water-holding capacity and reducing the cooking loss rate in the PPI group. Compared with the unfermented group, the addition of fermented PPI increased water-holding capacity by 13.26% and reduced the cooking loss rate by 36.60%, exhibiting the largest magnitude of change. Rheological analysis showed that peanut protein fractions (both unfermented and fermented) increased the final storage modulus, indicating enhanced stability of the protein network structure. Scanning electron microscopy revealed that different peanut proteins reduced the pore size and improved the uniformity of the chicken sausage gel structure. Notably, fermented peanut protein fractions promoted more intermolecular cross-linking in chicken mince, forming a denser and more compact spatial network structure.