Combating Sexual Harassment in Science Act of 2019 This bill addresses sexual harassment and gender harassment in the science, technology, engineering, and mathematics (STEM) fields by supporting research regarding such harassment and efforts to prevent and respond to such harassment. This bill directs the National Science Foundation (NSF) to award grants to institutions of higher education or nonprofit organizations (or their consortia) to expand research into sexual harassment and gender harassment in the STEM workforce, including students and trainees; and examine interventions for reducing the incidence and negative consequences of such harassment. The NSF must convene a working group composed of representatives of federal statistical agencies to develop questions on sexual harassment and gender harassment in STEM departments in order to gather national data on the prevalence, nature, and implications of such harassment in institutions of higher education. The NSF shall enter into agreements with the National Academies of Sciences, Engineering, and Medicine to (1) update a responsible conduct guide issued by the National Academies to include, among other things, updated professional standards of conduct in research and evidence-based practices for fostering a climate that is intolerant of sexual harassment and gender harassment; and (2) study the influence of such harassment in institutions of higher education on the career advancement of individuals in the STEM workforce. The National Science and Technology Council shall establish an interagency working group to coordinate the federal science agencies' efforts to reduce the prevalence of sexual harassment and gender harassment involving grant personnel. The Office of Science and Technology Policy must develop a uniform set of policy guidelines for such agencies to prevent and respond to reports of sexual harassment and gender harassment.