A meta-analysis compared kangaroo mother care (KMC) with conventional care in preterm or low birth weight infants during hospitalization. KMC significantly reduced in-hospital mortality [RR 0.791 (95% CI: 0.696–0.899), 95% CI: 0.679–0.925] and 28-day all-cause mortality [RR 0.9209, 95% CI: 0.605–1.085]. It was associated with shorter hospital stay [MD −0.809 (95% CI: −1.601 to −0.017), 95% CI: −3.219 to 1.601] and improved growth, such as accelerated weight, length, and head circumference gains. KMC reduced the risk of hypothermia, hyperthermia, apnea, sepsis, and necrotizing enterocolitis (all p < 0.05). Subgroup analyzes confirmed benefits especially in lower income countries. KMC is an effective and safe intervention to reduce mortality, shorten hospitalization, promote growth and prevent complications.