The challenges of a heme protein and enzyme-based H₂O₂ sensor was subdued by developing a highly sensitive and practically functional amperometric gold nanoparticles (Au NPs)/SnO₂ nanofibers (SnO₂ NFs) composite sensor. The composite was prepared by mixing multiporous SnO₂ NFs (diameter: 120–190 nm) with Au NPs (size: 3–5 nm). The synthesized Au NPs/SnO₂ NFs composite was subsequently coated on a glassy carbon electrode (GCE) and displayed a well-defined reduction peak during a cyclic voltammetry (CV) analysis. The SnO₂ NFs prevented the aggregation of Au NPs through its multiporous structure and enhanced the catalytic response by 1.6-fold. The SnO₂ NFs-supported GCE/Au NPs/SnO₂ NFs composite sensor demonstrated a very good catalytic activity during the reduction of hydrogen peroxide (H₂O₂) that displayed rapid amperometric behavior within 6.5 s. This sensor allowed for highly sensitive and selective detection. The sensitivity was 14.157 µA/mM, the linear detection range was from 49.98 µM to 3937.21 µM (R2 = 0.99577), and the lower limit of detection was 6.67 µM. Furthermore, the developed sensor exhibited acceptable reproducibility, repeatability, and stability over 41 days. In addition, the Au NPs/SnO₂ NFs composite sensor was tested for its ability to detect H₂O₂ in tap water, apple juice, Lactobacillus plantarum, Bacillus subtilis, and Escherichia coli. Therefore, this sensor would be useful due to its accuracy and sensitivity in detecting contaminants (H₂O₂) in commercial products.