A growing body of research conducted in general life settings has found positive associations between happiness and prosocial behavior. Unfortunately, equivalent studies in the workplace are lacking. Organizational citizenship behaviors (OCBs), the prosocial behaviors at work, have not been properly studied in relation to happiness, despite the positive consequences of both constructs for workers and companies. In response, our research aims to better understand this relationship from several angles. First, using a three-wave longitudinal design, we explored how OCBs and happiness are related to each other over time. Second, happiness was measured from a broad perspective, and three conceptualizations were adopted: the hedonic (e.g., positive affect and life satisfaction), the eudaimonic (e.g., relatedness and autonomy), and the flourishing (e.g., meaning and engagement) approaches. Thus, not only the prospective link between OCBs and happiness was tested, but it was also explored using the three models of happiness previously mentioned. Third, we conducted this longitudinal design in a less typical sample than previous research (i.e., Chile). We found results that supported our main hypotheses: (1) OCBs are prospective positive predictors of hedonic happiness, eudaimonic happiness, and flourishing; (2) the three models of happiness also prospectively predict OCBs. Our findings suggest that OCBs foster a broad range of happiness facets, which in turn fosters back the emergence of more OCBs, leading to a virtuous circle of prosociality and well-being in the workplace. This positive spiral benefits not only workers’ quality of life, but also organizations’ profitability and sustainability. Theoretical and applied implications for the field of Positive Organizational Psychology are discussed.