Background and purpose: Preparing a successful research proposal is one of the most complex skills required of professional scientists, yet this skill is rarely if ever, taught. A major goal of the National Research Mentoring Network (NRMN) in the United States (U.S.) is to support the professional advancement of postdoctoral fellows and junior faculty from diverse populations by offering intensive coaching in the development of grant proposals early in their careers. This article highlights the National Institutes of Health's (NIH) NRMN initiative to prepare diverse constituencies of early-stage biomedicine scientists for research careers by implementation of an evidence-based nationwide program of comprehensive grant writing and professional development. Program and key highlights: NRMN delivers four unique but complementary coaching models: the Proposal Preparation Program from the University of Minnesota (UMN); Grantwriters Coaching Groups from Northwestern University (NU); Grantwriting Uncovered: Maximizing Strategies, Help, Opportunities, Experiences from the University of Colorado Anschutz Medical Campus (UC) and Washington State University (WSU); and Steps Towards Academic Research from the University of North Texas Health Science Center (UNTHSC). Because these programs cater to scientists at different career stages, rather than employ a single approach, each is uniquely tailored to test its efficacy at the national level. The first two models prioritize scientists with reasonably well-developed research projects who are ready to write proposals for specific NIH research competitions. The other two models target postdoctoral fellows and early-career faculty who need more extensive guidance in proposal development plans. To achieve scalability, all programs also recruit faculty as Coaches-in-Training to learn approaches and acquire particular group facilitation skills required by each model. Implications: These efforts exemplify NRMN's potential to enhance the career development of diverse trainees on a national scale, building research skills, competitiveness for obtaining faculty positions and capacities that will result in high quality research proposals from a diverse pool of applicants, thereby advancing innovations in science and diversifying the U.S. biomedical workforce.