Exposure to heat stress (HS) detrimentally affects pig performance. This study explored whether a dietary phytogenic solution based on Capsicum spp. (PHY) could enhance the thermal tolerance of heat-stressed growing pigs. Forty-two individually housed pigs were randomly assigned to three treatments: thermoneutral pigs on a control diet (TN-C) and pigs subjected to HS fed the control diet either without (HS-C) or with supplemental PHY (HS-PHY). The TN-C group exhibited increased average daily gain (ADG) and feed intake (FI) compared to both HS-C (p < 0.01) and HS-PHY pigs (p < 0.05) and better feed efficiency compared to HS-C pigs only (p < 0.01). However, the HS-PHY pigs showed significantly higher FI (p < 0.01) and ADG (p < 0.05) compared to HS-C pigs. HS pigs displayed higher body temperatures (BTs) than TN pigs (p < 0.01), yet HS-PHY pigs experienced a lesser increase in BT compared to HS-C pigs (p < 0.05). Supplementation with PHY mitigated some effects of HS, increasing serum superoxide dismutase and catalase activity, reducing HSP90 expression in longissimus dorsi muscle, and elevating jejunal villus height compared to HS-C pigs (p < 0.05), reaching levels akin to TN-C pigs. Additionally, PHY supplementation resulted in lower serum urea levels than HS-C pigs (p < 0.01) and similar myosin gene expression to TN-C pigs (p > 0.1), suggesting enhanced amino acid post-absorptive utilization for lean tissue growth. In conclusion, dietary PHY supplementation partially offset the adverse effects of HS on pig performance by improving thermal tolerance.