The advent of positive psychology has triggered research into positive interventions, which focus on strengths instead of deficits. The present study aims to investigate the effects of gratitude and strengths-based interventions on happiness and depressive symptoms against a control group, as well as to explore personality traits as moderator variables of the potential effectiveness of these interventions. A total of 122 participants completed at least two stages of the research. Data were collected at three stages—baseline pre-test, post-intervention assessment, and 1-month follow-up assessment. The findings partially support the effectiveness of the gratitude and strengths-based interventions in increasing happiness and decreasing depressive symptoms compared to a control group. Two personality domains showed significance as moderator variables. More research is needed to enable a higher degree of control when administering these promising interventions.