By process of elimination, it is evident that the relative outsider Nick Carraway is the best person to tell the incredible story of Jay Gatsby.

Gatsby himself could never have told the story, because he could never tell it in an impartial way, and if he tried, the whole novel would have likely been a long list of everything he loves about Daisy, and diatribes about how lonely he is and how his wealth has not bought him happiness.

Next, let us consider Daisy Buchanan as a possible narrator. While beautiful and charming, Daisy lacks the depth of character that would be required to make her a good storyteller.

Tom Buchanan is distracted, to say the least, by the love affair that he is having on the side. He is also a domineering character, likely to make the story all about him had he been the storyteller.

Jordan Baker is both Nick's love interest and a well-known twister of the truth. As an audience, we would have fallen victim to Jordan's need to protect herself from unpleasant truths had she been the storyteller.

Nick Carraway, on the other hand, has many qualities which make him a great narrator. Being new to the area, he has not known Gatsby long and is able to describe Gatsby, and the events which occur, objectively. Over and above this, Nick is open-minded, tolerant and a good listener. In a nutshell, he's just the type of guy to which other characters would spill their secrets. He is the perfect choice for a narrator.

In order to tell the extraordinary story of Jay Gatsby, we need an outsider, someone who isn't part of that rarefied, privileged world in which the great man lives, moves, and has his being. We need someone honest, down-to-earth, someone who can always be relied upon to give us a brutally frank account of the often extraordinary events that unfold before us.

Enter Nick Carraway. He it is who's charged with the onerous responsibility of telling the tale of Jay Gatsby. He brings with him to the job a unique degree of objectivity that makes him especially reliable as a narrator. He has the kind of homely Midwestern common sense that provides some much-needed perspective to the often bizarre goings on among the beautiful people of East and West Egg.

Had Gatsby's extraordinary tale been told from this own perspective, then we wouldn't have found his story all that plausible. After all, if one looks at the bare facts of Jay's life they scarcely seem credible.

All the more reason, then, for us to have someone from an ordinary background, a decent, regular guy who can recount the remarkable details of a truly remarkable life and still be believed. That man, of course, as we have already seen, is Nick Carraway.

Arguably, Nick is the narrator of The Great Gatsby because he is an outsider. Nick is not from West or East Egg, for instance, and was, in fact, raised in the Midwest. In addition, Nick does not have the same wealth or status as Gatsby. 

Secondly, Nick is also the narrator of Gatsby's story because he is a non-judgemental type of person, as he admits in the opening chapter:

"I’m inclined to reserve all judgments, a habit that has opened up many curious natures to me."

This makes him the ideal person to tell Gatsby's story because he approaches it with honesty and objectivity. 

Moreover, when Nick finally gets an invitation to one of Gatsby's famous parties, he does not act like the other people there. He actively seeks Gatsby out, for example, and wants to know more about the man himself instead of the persona he has created. 

Nick tells the story of Jay Gatsby because he is arguably the most objective character in the novel. Also, since he has no previous knowledge of Gatsby, Nick can narrate in less of a chronological order than one would expect from those who have been acquainted with him.

As the readers learn about Gatsby in bits and pieces of background mixed with current knowledge, Nick tells readers about Gatsby in non-linear order that is typical of the Modernist movement in literature. In addition, this style of narration also seems more believable because this is the order in which one normally learns about someone. And, for Nick to repeat the fabrications of Jay--such as his war record--lends a trust factor to the narration because he is more naive about Gatsby than others. As he declares, "I am one of the few honest people that I have ever known."

In addition, Nick is a person whom others trust. However, Nick, too, becomes entangled as his own romantic naivete causes him to give more credibility to Gatsby than he would any other character or would an omniscient narrator. Yet, this credibility of Gatsby makes him "great," a man who believes that he can repeat the past and improve upon it.

With the assistance of Nick Carraway as narrator, Gatsby comes alive as a romantic hero. In Chapter Four, Nick narrates,

Then it had not been merely the stars to which he had aspired on that June night. He came alive to me, delivered suddenly from the womb of his purposeless splendor.

But, this romantic hero deteriorates for Nick, and he becomes disillusioned, thinking of returning to the Midwest where he can "run faster" and transcend the past and recreate the past.