Novel soluble cellulose-based nonionic biopolymers (CIs) with enhanced antimicrobial properties and nonleachability were successfully produced using a sustainable one-pot synthesis method. Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance H-spectrometer (¹H-NMR), X-ray Photoelectron Spectroscopy (XPS), and Energy Dispersive Spectroscopy (EDS) results demonstrated that the cellulose (MCC) molecules combined with indole-3-acetic acid (IAA) via esterification to produce CIs with abundant terminal indole groups. The degree of substitution of the prepared CI3 reached 1.85 when the molar ratio of IAA to MCC molecules was 4:1. The prepared CI samples were characterized using X-ray diffractometer (XRD), Scanning Electronic Microscopy (SEM), Thermogravimetric Analysis (TGA), and other analysis techniques. Results indicated that after the MCC was grafted with IAA, its crystallinity decreased and solubility increased. After blending CI3 with polycaprolactone (PCL) to form cellulose-based antimicrobial (PCL–CI) films, the films showed good compatibility, preferable biological cell activity, and low water vapor permeability. When the CI3 content was 10%, the tensile strength of the produced PCL–CI10 film reached 9.96 MPa. Moreover, the prepared PCL–CI films exhibited good nonleachability after being immersed in water for 5 d. The disk diffusion assay revealed that the CIs and PCL–CI films had good antimicrobial and bactericidal effects against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). The minimal inhibitory concentration was 5 μg disk⁻¹, significantly lower than that of traditional antibiotics and chitosan. The nonionic biopolymers are simple and efficient to prepare and ecofriendly as well as exhibit nontoxicity, good solubility, enhanced antimicrobial properties, and nonleachability, which can provide new ideas for developing natural biomass-based nonionic antimicrobial materials with potential applications in wound dressing, medical devices, and food packaging.