The first time Nick sees Gatsby is at the end of chapter 1; Nick is sitting outside his bungalow in West Egg after having dinner with Tom, Daisy, and Jordan in East Egg. He notices that he is not alone; a man has stepped outside Gatsby's mansion, and Nick correctly assumes that it is "Mr. Gatsby himself." Nick starts to call out to him but reconsiders because he intuits that Gatsby is "content to be alone." Nick watches as Gatsby extends his arms toward the bay that separates his house from Tom and Daisy's. Though he is about fifty feet away, Nick feels sure Gatsby is trembling. Nick looks in the direction of Gatsby's gaze and sees a green light that he thinks might be at the end of a dock. When Nick's gaze returns to where Gatsby was standing, he has disappeared.

Nick first sees Gatsby at the end of Chapter I.  He describes him as "standing with his hands in his pockets...."(25).  Nick is about to talk to call out to him, but decides not to when "he stretched his arms together toward the water in a curious way..."(26).  Nick then says, "...I could have sworn he was trembling" (26). Nick tells us that he is simply assuming this is Gatsby, but this does turn out to be a correct assumption.  Nick does not actually need Gatsby until the end of Chapter III, and there are a few passages that describe Gatsby, particularly very famous description of Gatsby's smile.