War, famine, political conflicts and environmental factors (e.g., climate change) have increased the flow of immigrants into several European countries. Immigrants' integration represents one of the most important challenges to our globalized society. Previous research has pointed out that social-dominant people show negative reactions towards immigrants. The present research is aimed at expanding and consolidating previous knowledge about immigrants' research by proposing that: (i) citizens' happiness is related to a favorable attitude towards immigrants; and (ii) social dominance orientation is related to attitude towards immigrants through happiness. In this study, a large sample recruited across different European countries (European Social Survey 2014 data, N = 40,185) has been considered. Measures of social dominance orientation, happiness and attitude towards immigrants have been assessed. Results showed that people's happiness is related to favorable attitudes towards immigrants. Moreover, these results also showed the mediating role of happiness in the relationship between social dominance and attitude towards immigrants. Implications for future studies and policy strategies to support immigrants' integration are discussed.