Diary interventions have been shown to increase positive thinking and have profound effects on wellbeing. One example is Seligman et al., (2005), where after participants journaled ‘3 Good Things’ and their causal attributions for 5-days, significant gains in wellbeing and decreases in depressive symptomology were observed at 6-month follow-up. Two potential underlying mechanisms involved were positive thinking and an individual’s sense of control over their actions (e.g. internal Locus of Control; LoC). Independently both of these have been shown to improve wellbeing; it is unclear though which of these mechanisms may be driving the greatest wellbeing gains in positive events diaries. The current study aimed to disentangle these, alongside validating a novel ‘LoC’ diary. Over 7-days, participants engaged with either a Positive Events (PE), LoC or placebo control diary. At pre-test, 1-week post-test and 1-month follow-up, individuals were assessed on their levels of self-reported wellbeing, motivation and perceptions of control. Results showed that both the PE and LoC diaries had significant short-term effects on depressive symptomology, whilst the LoC diary improved long-term perceptions of control. The current investigations add credence to the use of positive event diaries, alongside showing promise for the development of a novel LoC diary.