Jay Gatsby wore a Longines Evidenza. Or maybe he didn't. Perhaps he wore a Rolex, or maybe a Patek Philippe, or a Gruen. And that's sort of the point.
The Great Gatsby is F. Scott Fitzgerald's magnum opus, a story about love, obsession, greed, and the roaring 20's. The story follows Nick Carraway, an insurance salesman who moves to the fictional Long Island suburb of "West Egg", and rents a modest house next to the mansion of a reclusive and mysterious millionaire. Carraway notices that the millionaire, rumored to be Jay Gatsby, throws lavish parties, but rarely attends them. Over the course of the summer, Nick is invited to one of Gatsby's parties, where he meets the man himself. Gatsby says he recognizes Nick from their same division in WWI and confesses that he is in love with Nick's cousin Daisy.
In the end, we find that the money and parties and all of the extravagance with which the great Gatsby lives his life is all a ruse so that he can charm Daisy and make her fall in love with him.
To this end, we see a lot of extravagant wealth in Jay Gatsby's life, but not a lot of it is finely detailed. Specifically, his watch is never mentioned. But because he's a fictional character, you can imagine on him whatever watch you would think fits his persona.
Robert Redford took the role of Jay Gatsby to the big screen in 1974. In his depiction, Gatsby doesn't wear a wristwatch at all. Instead, he wears a nice pocket watch, though we don't really see it and have no way of knowing what kind of watch it really is.
Dicaprio’s take on Jay Gatsby wore another very plausible watch for the millionaire: A silver, square-faced art deco watch – a very JFK timepiece. Art Deco was a very popular style in the 1920’s that found it’s way into everything from architecture to interior design. The Art Deco style symbolized technology and progress, and later became intrinsically connected with opulent wealth. Because of this, it is very likely that Jay Gatsby, if he wore a wristwatch, would have worn an art deco style wristwatch.
The watch that Dicaprio wears in the movie, however, is not a real watch. There are multiple shots of the watch from which you should be able to identify it, but upon inspection the watch does not appear to have any brand markings or engravings. Other than the tallies and hands, in fact, the watch is completely blank and devoid of any kind of mark. Tiffany & Co., in conjunction with the movie, released a limited run "Jay Gatsby Collection" of men and women's jewelry, but there was not a watch in the set.
If you're looking for a similar watch to the one featured in the movie, we recommend the Longines Evidenza.