Informal learning activities and workplace learning constitute a substantial part of a PhD student's knowledge as an adult. It is essential to define the concept of workplace learning and the roles and responsibilities of doctoral students clearly and transparently while explaining how doctoral courses and workplace experience correspond to each other. Learning, in this sense, manifests itself in everyday practices of work and social contexts. In this vein, this study explores the informal workplace learning experiences of PhD students working in university settings with different job titles to offer new contributions to the literature on informal adult learning. Data were collected through in-depth semi-structured interviews with 10 PhD students who were employed in different university settings. Thematic analysis was used to interpret the data. The findings revealed that doctoral students working at universities learn at work by participating in various work-related tasks, collaborating with their colleagues and other people in these settings, and encountering new challenges that provide learning opportunities for them. The unexpected challenges, tasks, and office conversations that are not directly related to the work play key roles in the learning and skill acquisition of this target group. Doctoral students are among the intellectual assets of their home countries and the world. In addition to their formal graduate education, understanding their informal learning and how they learn in their workplaces will be of value for both academia and organisational effectiveness. In parallel to this, the idea of educating the qualified labour force of the future through graduate education has become a fundamental issue for every country in efforts to compete on a global scale. Investigating this phenomenon in different university contexts and area-specific programs would contribute to a better understanding of the informal workplace learning experiences of doctoral students. Graduate program planners could consider integrating the informal learning processes of graduate students into future graduate programs.