Ernest Miller Hemingway (July 21, 1899 - July 2, 1961) is one of the most widely read American novelist of the 19th century, whose works have been variously interpreted. His fiction was influenced by different sociological, political and psychological trends of the time. The adventures of his personal life inspired some of the fascinating stories in his fiction. A Farewell to Arms projects the concept of individual struggle in the face of stiff resistance. His protagonist helplessly strives to define his existence; he, however, miserably fails in his struggle for actualizing his existence. But ultimately, he learns the secret of a meaningful existence. This study traces these elements of existentialist philosophy and examines its influence on the art of Hemingway. Although his views are also influenced and modified by the trends of the time, the influence of existentialist philosophy is vividly visible in all his writings. The paper analyzes the major works of Hemingway, particularly his famous novel A Farewell to Arms, in the light of existentialism. It specifically focuses on the rise and fall of the hero and heroine in the novel when they try to define their existence in this free and void world.