High blood pressure and excess weight during pregnancy can have adverse outcomes. This randomized controlled trial evaluated the effects of a nurse-led smartphone application-based lifestyle intervention on blood pressure, body weight, and pregnancy outcomes in pregnant women with gestational hypertension between August and December 2023. Pregnant women, between 20 and 28 weeks of gestation, were allocated to the intervention or control group. Control group (n = 99) received standard high-risk pregnancy management, while intervention group (n = 96) also received lifestyle guidance via a nurse-led smartphone application. Intervention group experienced longer gestations (p = 0.007), higher neonatal weights (p = 0.028), and lower incidences of pre-eclampsia (p <
0.002), small for gestational age infants (p = 0.003), and preterm births (p = 0.023) compared to control group. The mixed-effect models for repeated measures showed that the nurse-led smartphone application intervention had no impact on body mass index, while significantly reducing systolic and diastolic blood pressure measurements (β = -1.666, 95% confidence interval, CI: -2.814 to -0.519, p = 0.005 and β = -2.247, 95% CI: -3.349 to -1.145, p <
0.002, respectively). Both systolic and diastolic blood pressures showed a downward trend from 28 weeks (p <
0.05). The nurse-led smartphone application-based lifestyle intervention significantly reduced adverse pregnancy outcomes and positively influenced blood pressure management in pregnant women with gestational hypertension.