Participation in designated learning opportunities and engagement in workplace learning are very different kinds of professional learning activities: Whereas the former takes place in organised, predefined settings with intended learning objectives, the latter mostly arises as a by-product through everyday experiences at work. Yet, empirical and theoretical models often do not sufficiently differentiate between these two kinds of learning activities. The main goal in the present study is to test whether the two discrete learning activities are indeed facilitated in different ways and by different antecedents. The results of a multi-wave diary study with a sample of 229 German employees show that engagement in workplace learning is not influenced by conscious beliefs connected to learning, which play a central role in most theoretical models explaining participation in designated learning opportunities, underlining the need for an autonomous theory of workplace learning. Furthermore, the current study shows the strong direct, indirect, and moderating influence of organisational learning culture on both kinds of professional learning activities. Possible implications for practitioners to put greater emphasis on organisational factors when designing learning opportunities are discussed.