Short Message Service (SMS)-delivered behaviour change interventions are frequently used to support weight management. This systematic review examines the effectiveness of SMS-delivered behaviour change interventions for weight management. Electronic databases were searched for randomised controlled trials (RCTs) comparing SMS-delivered adult weight management interventions to control groups, published between 1990 and 2018. Weight change was examined using random effects meta-analyses at intervention cessation and postintervention follow-up. Subgroup analyses examined intervention duration, SMS frequency, theory use, SMS interactivity, and SMS tailoring. Fifteen studies met inclusion criteria (2705 participants). For weight loss interventions (n = 12, 1977 participants), the mean difference in weight change was −2.28 kg (95% confidence interval [CI] −3.17 to −1.36 kg). No studies reported postintervention follow-up. For weight loss maintenance interventions (n = 3, 728 participants), the mean difference in weight change was −0.68 kg (95% CI, −1.31 to −0.05 kg), and postintervention follow-up (n = 2, 498 participants) effects were −0.57 kg (95% CI, −1.67 to 0.53 kg). No subgroup differences were found. SMS-delivered behaviour change interventions for weight loss led to significant small to moderate weight loss and weight loss maintenance compared with control groups. Evidence on long-term effects is limited. SMS-delivered behaviour change interventions are a potentially effective and scalable intervention option for obesity treatment.