Objectives. To assess the effect of 2-way short message service (SMS) with a nurse on postpartum contraceptive use among individual women and couples. Methods. From 2016 to 2017, we conducted a randomized controlled trial at 2 public hospitals in western Kenya. We assigned eligible pregnant women to receive 2-way SMS with a nurse or no SMS, with the option to include male partners. We delivered automated family planning-focused SMS messages weekly until 6 months postpartum. Women and men receiving SMS could interact with nurses via SMS. In intention-to-treat analysis, we compared highly effective contraceptive (HEC) use at 6 months postpartum between groups using the χ2 test. We used Poisson regression in adjusted analysis. Results. We randomized 260 women to 2-way SMS or control, and we enrolled 103 male partners. At 6 months postpartum, 69.9% women receiving SMS reported HEC use, compared with 57.4% in control (relative risk = 1.22; 95% confidence interval [CI] = 1.01, 1.47; P = .04). In analysis adjusted for baseline demographic differences, the adjusted relative risk for HEC use in the SMS group was 1.26 (95% CI = 1.04, 1.52; P = .02). Conclusions. Two-way SMS with a nurse, including optional male participation, increased postpartum contraceptive use. Trial Registration. ClinicalTrials.gov; identifier: NCT02781714.