Self-regulated training behaviours plays a vital role in athletes’ physical and mental sporting development. The purpose of the present study was to investigate the mediating role of self-regulated training behaviours (self and coach rated) on the relationship between self-reported Mental Toughness (MT) and coaches perceptions of swimmers Mentally Tough behaviour (MTb) in competition. A second purpose of the study was to examine how discrepancies in coach and athlete perceptions of training behaviours related to coach perceptions of swimmers MTb in competition. A sample of 12 swimming coaches (11 men and 1 women) and 208 of their competitive swimmers (86 men and 122 women) participated in the study. The swimmers completed self-report assessments of MT and self-regulated training behaviours. The coaches completed questionnaires regarding observations of their swimmers MTb in competition and a smaller pool of items from the athletes self-regulated training behaviours questionnaire. Findings supported our hypotheses that MT was positively related to self-regulated training behaviours (self and coach rated) and training behaviours was positively related to coach rated MTb. Further, self-regulated training behaviours (β = 0.12; CI = 0.05 – 0.20) and coach rated perceptions of training behaviours (β = 0.07; CI = 0.03 – 0.13) mediated the relationship between self-report MT and coach rated MTb in competition. Finally, a significant amount of variance in MTb was accounted for (23%) only when there was agreement between the coach and the athlete regarding the level of self-regulated training behaviours. We recommend that future research examines what specific types of training behaviours positively influence MT.