Fitzgerald was commissioned a second lieutenant in the infantry and assigned to Camp Sheridan outside of Montgomery, Alabama. While at a country club, Fitzgerald met and fell in love with Zelda Sayre (1900–1948), the daughter of an Alabama Supreme Court justice and the "golden girl," in Fitzgerald's terms, of Montgomery youth society. The war ended in 1918, before Fitzgerald was ever deployed, and upon his discharge he moved to New York City hoping to launch a career in advertising that would be lucrative enough to convince Zelda to marry him. He worked for the Barron Collier advertising agency, living in a single room at 200 Claremont Avenue in the Morningside Heights neighborhood on Manhattan's west side.
Zelda accepted his marriage proposal, but after some time and despite working at an advertising firm and writing short stories, he was unable to convince her that he would be able to support her, leading her to break off the engagement. Fitzgerald returned to his parents' house at 599 Summit Avenue, on Cathedral Hill, in St. Paul, to revise The Romantic Egoist, recast as This Side of Paradise, a semi-autobiographical account of Fitzgerald's undergraduate years at Princeton. Fitzgerald was so short of money that he took up a job repairing car roofs. His revised novel was accepted by Scribner's in the fall of 1919 and was published on March 26, 1920 and became an instant success, selling 41,075 copies in the first year. It launched Fitzgerald's career as a writer and provided a steady income suitable to Zelda's needs. They resumed their engagement and were married at St. Patrick's Cathedral, New York. Their daughter and only child, Frances Scott "Scottie" Fitzgerald, was born on October 26, 1921.