Whole-plant soybean silage (WPSS) is a potential high-protein roughage source for ruminant diets. However, WPSS can be difficult to ensile and fermentation is a challenge. This study was conducted to evaluate the effect of chitosan and microbial inoculants on fermentation profile, fermentation losses, chemical composition, and in vitro degradation of WPSS. Forty experimental silos (PVC tubing with 28 cm i.d. and 25 cm height) were produced. Soybean plants from 10 plots were ensiled in a completely randomized block design to evaluate the following treatments: (1) control (CON): WPSS without additives; (2) chitosan (CHI): WPSS additive with 6 g/kg DM of chitosan; (3) LBB: WPSS treated with 5.0 × 107 colony-forming units (CFU) of Lactobacillus buchneri (NCIM 40788) per kg of fresh matter and (4) LPP: WPSS treated with 1.6 × 108 CFU of Lactobacillus plantarum and 1.6 × 108 CFU of Pediococcus acidilactici per kg of fresh matter. Silos were opened 120 days after ensiling. Microbial inoculants reduced silage pH, whereas LPP-treated silos showed the lowest concentration of NH3-N, ethanol, butyric, acetic, branched-chain, and propionic organic acids. LBB-treatment decreased lactic acid bacteria (LAB) count relative to other treatments, and LPP-treatment showed the lowest fermentation losses, improving dry matter (DM) recovery. Relative to other treatments, LPP increased silage DM, organic matter, and decreased acid detergent insoluble crude protein (CP), improving DM and neutral detergent fibre in vitro degradation. Treatments showed no effect on silage aerobic stability. Thus, LPP-treatment improves fermentation profile, reduces fermentation losses, and increases the nutritional value of WPSS.