Understanding how environmental factors regulate photosynthetic energy partitioning is crucial for enhancing crop resilience in future climates. This study investigated the light-response dynamics of sweet sorghum (Sorghum bicolor L. Moench) leaves under combinations of CO₂ concentrations (250, 410, and 550 μmol mol⁻¹) and temperatures (30 °C and 35 °C), using integrated chlorophyll fluorescence measurements and mechanistic photosynthesis modeling. Our results revealed that elevating CO₂ from 250 to 550 μmol mol⁻¹ significantly increased the maximum electron transport rate (J_max) by up to 57%, and enhanced the effective light absorption cross-section (σ′_ik) by 64% under high light and elevated temperature (35 °C), indicating improved photochemical efficiency and light-harvesting capability. Concurrently, these adjustments reduced PSII down-regulation. Increased temperature stimulated thermal dissipation, reflected in a rise in non-photochemical quenching (NPQ) by 0.13–0.26 units, accompanied by a reduction in the number of excited-state pigment molecules (N_k) by 20–33%. The strongly coordinated responses between quantum yield (Φ_PSII) and σ′_ik highlight a dynamic balance among photochemistry, heat dissipation, and fluorescence. These findings elucidate the synergistic photoprotective and energy-partitioning strategies that sweet sorghum employs under combined CO₂ enrichment and heat stress, providing mechanistic insights for optimizing photosynthetic performance in C₄ crops in a changing climate.