This study is aimed at exploring the types, meaning and functions of lexical presupposition triggers employed in the narrative tiers in the portrayal of Gatsby and Daisy's characters in Fitzgerald's The Great Gatsby. To fulfill such aim, the researcher adapts a model proposed by Li (2010) and Du (2012) based on the theory of presupposition put forward by Levinson (1983) and Yule (1996). Through the descriptive qualitative approach, the data analysis shows that eight types of lexical triggers out of the nine studied are found—verbs of judging are not employed—and the most frequently employed one is the possessive. The analysis also brings into light the descriptive, narrative, thematic and symbolic purposes of these triggers along with their different functions. The results detect Fitzgerald's bias towards what his characters represent, and reveal that presupposition present, to a greater extent, the atmosphere of illusion versus reality that dominates the novel.