The research team explored UK trainee sport psychologists’ perspectives on developing professional judgment and decision-making (PJDM) expertise during their British Psychological Society (BPS) Qualification in Sport and Exercise Psychology (QSEP; Stage 2). An assorted analysis approach was adopted to combine an existing longitudinal qualitative data set with the collection and analysis of a new qualitative data set. Participants (female, n = 1; and male, n = 6) were interviewed 4 times over a 3-year training period, at minimum yearly intervals. Interviews were transcribed verbatim, and reflexive thematic analysis applied to transcripts using the theoretical concepts of PJDM. Experience, analytical reasoning, and observation of other practitioners’ practice was useful for developing PJDM expertise. PJDM expertise might be optimised through the use of knowledge elicitation principles. For example, supervisors could embed critical cues within the anecdotes they share to expand the experience base that trainees can draw from when making decisions.