Purpose: This study aims to explore the motivation and satisfaction of part-time PhD students in the USA through the lens of self-determination theory (SDT). Design/methodology/approach: Following an explanatory sequential mixed methods design, data sources consisted of a survey (N = 100) and focus groups (N = 20) of part-time PhD students. Findings: Findings suggest that part-time PhD students achieve greater satisfaction when they are autonomously motivated. Part-time PhD student satisfaction may be increased through shifting motivation from an external to an internal locus of control, such as when doctoral work is framed within the context of solving practice-based problems. Facilitating this change requires those involved in the practice of research doctoral education to work toward satisfying students' innate needs of autonomy, competence and relatedness with others, yet many part-time PhD students describe experiences within their doctoral education that do not meet these needs. Implications for research and practice are presented. Originality/value: This paper tests the applicability of SDT, a widely used theory in doctoral studies, to part-time PhD students, an understudied student population in the USA.