The study examined the effects of a microencapsulated complex of biofactors and antioxidants (P(BF + AOx)) on growth and health status of broiler chickens challenged with cold stress. Day-old broilers were allotted to four treatments in a 2 × 2 factorial design with two dietary treatments: (1) Control (CON; corn–wheat–soybean-based) and (2) CON + 0.015% P(BF + AOx), and two thermal treatments: (1) Thermoneutral (TN; 29 °C ± 1 on days 8–10, 54 h) and (2) Cold stress (CS; 20 °C on days 8–10, 54 h). Treatments were allocated to six replicates, with eight chicks/replicate. Growth performance was measured weekly from days 0–21. On day 14, two birds/cage were euthanized. Cold stress reduced (P < 0.05) total antioxidant capacity (TAC), serum IgM, jejunal villus height (VH), villus width (VW), and VH:crypt depth (VH:CD). Irrespective of CS, P(BF + AOx) improved (P < 0.05) feed intake (631 vs. 592 g/bird), body weight (BW) (383 vs. 349 g/bird), BW gain (337 vs. 301 g/bird) up to day 14, and plasma TAC. Regardless of the challenge model, P(BF + AOx) increased (P < 0.05) duodenal VW, VH:CD, jejunal, and ileal VH:CD, and the relative abundance of cecal Intestinimonas and Colidextribacteria, compared to the CON. In conclusion, CS altered broiler blood parameters and gut morphology, but 0.015% P(BF + AOx) improved early life growth performance, TAC, and gut health, irrespective of CS, suggesting that it could be an effective strategy to support overall health and performance.