Converting carbon dioxide (CO₂) into high-value-added chemicals using solar energy is a promising approach to reducing carbon dioxide emissions; however, single photocatalysts suffer from quick the recombination of photogenerated electron–hole pairs and poor photoredox ability. Herein, silver (Ag) nanoparticles featuring with localized surface plasmon resonance (LSPR) are combined with g-C₃N₄ to form a Schottky junction for photothermal catalytic CO₂ reduction. The Ag/g-C₃N₄ exhibits higher photocatalytic CO₂ reduction activity under UV-vis light; the CH₄ and CO evolution rates are 10.44 and 88.79 µmol·h⁻¹·g⁻¹, respectively. Enhanced photocatalytic CO₂ reduction performances are attributed to efficient hot electron transfer in the Ag/g-C₃N₄ Schottky junction. LSPR-induced hot electrons from Ag nanoparticles improve the local reaction temperature and promote the separation and transfer of photogenerated electron–hole pairs. The charge carrier transfer route was investigated by in situ irradiated X-ray photoelectron spectroscopy (XPS). The three-dimensional finite-difference time-domain (3D-FDTD) method verified the strong electromagnetic field at the interface between Ag and g-C₃N₄. The photothermal catalytic CO₂ reduction pathway of Ag/g-C₃N₄ was investigated using in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS). This study examines hot electron transfer in the Ag/g-C₃N₄ Schottky junction and provides a feasible way to design a plasmonic metal/polymer semiconductor Schottky junction for photothermal catalytic CO₂ reduction.