Abstract Background Psoriasis affects at least 60 million people worldwide, and 80% also live with overweight or obesity. Excess weight increases susceptibility to psoriasis and is associated with more severe disease. Objective To evaluate the impact of weight‐loss interventions on psoriasis severity (Psoriasis Area and Severity Index [PASI], PASI50, PASI75, PASI100 [50%/75%/100% reduction in baseline PASI, respectively]) and quality of life (Dermatology Life Quality Index [DLQI]). Methods We systematically searched five databases and two trial registries (inception to 03/09/2025). Outcomes were informed by patient focus‐group discussions. Randomized controlled trials (RCTs) in adults with psoriasis, comparing any weight‐loss intervention versus usual care or a lower‐intensity weight‐loss intervention, were included. Studies had to report a change in weight and ≥1 psoriasis severity or quality‐of‐life measure. Random effects meta‐analyses were used. Results Thirteen RCTs (1145 participants) with 14 comparisons were included. Eleven interventions advised dietary changes, of which four included physical activity. Three used weight‐loss medications. Across 14 comparisons ( n = 1145, mean difference (MD) in weight change: −6.7 kg), weight‐loss interventions produced a greater reduction in PASI versus control: MD −2.5 (95%CI: −3.8 to −1.1, I 2 = 85.2%). We found a significant effect of weight‐loss interventions on the likelihood of achieving PASI75 (RR = 1.6, 95%CI: 1.1–2.2, I 2 = 22.6% [based on six comparisons, n = 681, MD in weight change: −7.3 kg]). There was no statistically significant effect of the interventions on the likelihood of achieving PASI50 (RR = 1.5, 95%CI: 0.9–2.4, I 2 = 72.8% [based on four comparisons, n = 509, MD in weight change: −4.0 kg]) or PASI100 (RR = 1.6, 95%CI: 0.3–9.7, I 2 = 0.0% [based on two comparisons, n = 334, MD in weight change: −5.2 kg]), but both analyses were limited by few studies. Across seven comparisons ( n = 364; MD in weight change −7.8 kg), weight‐loss interventions were associated with a significant improvement in DLQI compared to control: MD −5.0 (95%CI: −9.7 to −0.3, I 2 = 96.0%). Conclusion High‐certainty evidence suggests weight‐loss interventions can improve psoriasis severity and quality of life, and should be considered as part of routine treatment.