F. Scott Fitzgerald completed and published four novels in his lifetime. They were This Side of Paradise (1920), The Beautiful and Damned (1922), The Great Gatsby (1925), and Tender Is the Night (1934).
The number can be confusing because Fitzgerald worked on a fifth novel, The Last Tycoon, during the final years of his life. He died in 1940 before finishing it, and the manuscript was published posthumously in 1941 as an unfinished work. It therefore does not count among the novels he completed and published himself.
Fitzgerald also wrote numerous short stories, essays, and story collections, but those are separate from his novels. The Great Gatsby eventually became his most celebrated book, although it was not initially a major commercial success. Tender Is the Night was his fourth and final completed novel, drawing partly on his experiences with expatriate life, alcoholism, and Zelda Fitzgerald's mental illness.