Throughout the history of the United States, there have been many social movements that have resulted in an array of historic societal outcomes—ranging from the end of racial segregation to women’s voting rights to the legalization of same-sex marriages. Despite the positive outcomes derived from political activism, many psychologists have struggled with how to advocate for social justice while maintaining their professional responsibilities and ethical boundaries. The current article reviews the historical ways that psychologists have participated in political movements—from the use of psychological research in landmark U.S. Supreme Court cases to psychologist-led pushes for policy changes in psychology, medicine, and other mental health related fields. Next, a critical review provides some of the major controversies or dilemmas regarding psychology, social justice, and political participation—including (a) ethical concerns and professional boundaries, (b) the utility of political neutrality in psychology, (c) psychologists’ balance and self-care, (d) psychologists’ lack of advocacy training, and (e) beliefs concerning the role of social justice advocacy in psychology. Finally, the article concludes with a discussion of the concept “psychologist–activist”—highlighting the many ways that psychologists across various subfields and institutions can combat oppression on individual, interpersonal, group, and institutional levels.