Owing to the importance of employee psychological well-being for a variety of work- and non-work-related outcomes, practitioners and scholars have begun to broaden the scope of workplace well-being interventions by incorporating principles from positive psychology. Among such positive interventions, gratitude exercises have arguably emerged as the “gold standard” practice, with much research pointing to their effectiveness. However, existing workplace interventions lack a true (i.e., no intervention) control group, and effects have been observed for some—but not all—outcomes tested. Therefore, the purpose of this brief report was to conduct a concise but methodologically rigorous evaluation of the effectiveness of 2 positive psychology workplace interventions in improving employee affect, and to examine potential moderators of intervention effectiveness. Ninety-two employees in a large social services agency were assigned to (a) a gratitude intervention, (b) an intervention in which participants alternated between the gratitude activity and one involving increasing social connectedness, or (c) a wait list control condition, for 1 month. Neither intervention produced a main effect on any of the 3 affective outcomes measured. However, agreeableness, conscientiousness, and job tenure were significant moderators of intervention effectiveness. We discuss the implications of these preliminary results in an effort to advance the literature on workplace positive psychology interventions.