Chemoselective hydrodeoxygenation of vanillin is of great importance in converting biomass into high value-added chemicals. Herein, we describe a facile photochemical route to access palladium single atoms and clusters supported on silicoaluminophosphate-31 (SAPO-31) as a highly active, chemoselective, and reusable catalyst for hydrodeoxygenation of vanillin. Characterizations by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, extended X-ray absorption fine structure measurement, and CO-absorbed diffuse reflectance infrared Fourier transform spectroscopy reveal the atomically dispersed palladium single atoms and clusters are loosely bonded and randomly dispersed, without forming strong palladium-palladium metallic bonding, over the SAPO-31 support. This catalyst, with a full metal availability to the reactants, exhibits exceptional catalytic activity (TOF: 3,000 h⁻¹, Yield: > 99%) in the hydrodeoxygenation of vanillin toward 2-methoxy-4-methylphenol (MMP) under mild conditions (1 atm, 80 °C, 30 min), along with excellent stability, scalability (up to 100-fold), and wide substrate scope. The superior catalytic performance can be attributed to the synergistic effect of the positively charged palladium single atoms and fully exposed clusters, as well as the strong metal-support interactions. This work may offer a new avenue for the design and synthesis of fully exposed metal catalysts with targeted functionalities.