Background: Excessive weight gain among young adult women age 18-45 years is an alarming and overlooked trend that must be addressed to reverse the epidemics of obesity and chronic disease. During this vulnerable period, women tend to gain disproportionally large amounts of weight compared to men and to other life periods. Healthy Eating and Active Living Taught at Home (HEALTH) is a lifestyle modification intervention developed in partnership with Parents as Teachers (PAT), a national home visiting, community-based organization with significant reach in this population. HEALTH prevented weight gain, promoted sustained weight loss, and reduced waist circumference. PAT provides parent-child education and services free of charge to nearly 170,000 families through up to 25 free home visits per year until the child enters kindergarten. Methods: This study extends effectiveness findings with a pragmatic cluster randomized controlled trial to evaluate dissemination and implementation (D&I) of HEALTH across three levels (mother, parent educator, PAT site). The trial will evaluate the effect of HEALTH and the HEALTH training curriculum (implementation strategy) on weight among mothers with overweight and obesity across the USA (N = 252 HEALTH; N = 252 usual care). Parent educators from 28 existing PAT sites (14 HEALTH, 14 usual care) will receive the HEALTH training curriculum through PAT National Center, using PAT's existing training infrastructure, as a continuing education opportunity. An extensive evaluation, guided by RE-AIM (Reach, Effectiveness, Adoption, Implementation, Maintenance), will determine implementation outcomes (acceptability, adoption, appropriateness, feasibility, fidelity, and adaptation) at the parent educator level. The Conceptual Framework for Implementation Research will characterize determinants that influence HEALTH D&I at three levels: mother, parent educator, and PAT site to enhance external validity (reach and maintenance). Discussion: Embedding intervention content within existing delivery channels can help expand the reach of evidence-based interventions. Interventions, which have been adapted, can still be effective even if the effect is reduced and can still achieve population impact by reaching a broader set of the population. The current study will build on this to test not only the effectiveness of HEALTH in real-world PAT implementation nationwide, but also elements critical to D&I, implementation outcomes, and the context for implementation.