She was raised in St. Louis, Missouri and married Ernest Hemingway on September 3, 1921. Together they moved to Paris, France, and in the fall of 1923, as Hadley approached the term of her pregnancy, they returned westward so that their child could be born in North America. On October 10, 1923, Hadley gave birth to John Hadley Nicanor Hemingway in Toronto, Canada. John was nicknamed "Bumby" and "Jack", and later fathered three daughters, including actresses Margaux Hemingway and Mariel Hemingway.
In January 1924 the Hemingway family returned to Paris. Hadley and Hemingway had many adventures together as members of "The Lost Generation," as Gertrude Stein called the expatriates living in Paris. Hemingway recounted these days in his non-fiction book A Moveable Feast. It covered the years 1921–1926 and it recounts the days of the "struggling artist", Hemingway and wife Hadley, and their adventures in the sidewalk cafe society of Paris; and their trips to Switzerland, Austria, and Spain.