Dropout rates remain persistently high in doctoral programmes (up to 50%), particularly in the online modalities. Students in these programmes are largely non-traditional; namely, mature-aged; studying online and part-time; and balancing their academic, working, and family life. There is very little research done on the experiences and perceptions of this particular group of doctoral students. The objective of this research is to explore the reasons why UOC’s part-time PhD students persist and achieve their academic goals or, alternatively, drop out before degree completion. To this end, we will use a mixed methods approach, adopting a sequential exploratory design. The first phase of this research will be qualitative and based on in-depth, semi-structured interviews. Thematic analysis will be employed to analyse the results. The second phase will be quantitative and based on a survey built on the findings of the previous phase. Statistical analysis will be utilised to analyse the data. Integration of both phases’ results will follow. Recommendations aimed at improving part-time doctoral students’ satisfaction and retention will be derived. Although focused on a single institution, this research might be relevant to other higher education institutions in a context of growing adoption of blended and fully online doctoral programmes.