Consumer awareness about environmental problems is important in guiding their purchasing decisions. The aim of this research is to validate the moderating effect of environmental concern in two relationships: between celebrity–brand congruity and attitudes toward the brand and, between celebrity–brand congruity and purchase intentions, specifically when consumers are exposed to green advertising including a celebrity endorser. The data were collected via an online survey with young North American and Chilean people. Structural equation modeling was used to test hypotheses in both samples. The results show that the only endorser characteristic relevant to the model is celebrity–brand congruity and its relationship with environmental concern (β = 0.23 for North Americans and β = 0.35 for Chileans with p < 0.05). In conclusion, the consumers evaluate congruence between celebrity and brand based on their concern about environment, then consider brand ethicality, and later brand credibility, which generates an attitude toward the brand and purchase intention. Therefore, identifying the consumers environmental concern is key to developing an effective advertisement with an appropriate celebrity. This research helps to understand the green-marketing literature in a more detailed way, due to this moderating variable capable of enhancing purchase intentions of consumers.