Mary Welsh Hemingway (née Welsh; April 5, 1908 – November 26, 1986) was an American journalist and author who was the fourth wife and widow of Ernest Hemingway.

Born in Walker, Minnesota, Welsh was a daughter of a lumberman. In 1938, she married Lawrence Miller Cook, a drama student from Ohio. Their life together was short and they soon separated. After the separation, Mary moved to Chicago and began working at the Chicago Daily News, where she met Will Lang Jr. The two formed a friendship and worked together on several assignments. A career move presented itself during a vacation in London when Mary started a new job at the London Daily Express. The position soon brought her assignments in Paris during the years preceding World War II.

After the fall of France in 1940, Welsh returned to London as a base to cover the events of the war. She also attended and reported on the press conferences of Winston Churchill.

During the war she married her second husband, Australian journalist Noel Monks.

In 1944, Welsh met American author Ernest Hemingway while covering the war in London, and they became intimate. In 1945, she divorced Noel Monks, and in March 1946, she married Hemingway in a ceremony in Cuba.

Welsh's and Hemingway's temperaments were well-suited to one another; while Hemingway's previous wife, war correspondent Martha Gellhorn, had chafed against his efforts to assert his dominance, Mary Welsh wrote, "I wanted him to be the Master, to be stronger and cleverer than I; to remember constantly how big he was and how small I was."

In August 1946, Welsh had a miscarriage due to an ectopic pregnancy.

After their wedding, Mary lived with Hemingway in Cuba for many years and, after 1959, in Ketchum, Idaho. In 1958, while still in Cuba, she appeared in a non-speaking role, along with her husband, in cameo appearances in John Sturges's film version of Hemingway's 1952 novella, The Old Man and the Sea. Hemingway portrayed a gambler in the film, and Mary an American tourist.