John Fisher Preston Jr., was born on November 5, 1872, in Baltimore, to a prominent lawyer. He graduated from the Baltimore City College in 1890, and attended the United States Military Academy from June 17, 1890 until he graduated 21st in the class of 1894 on June 12. He was commissioned in the army as a second lieutenant of infantry in the 16th Infantry. Preston then served on garrison duty at Fort Douglas, Utah, from September 30, 1894 to October 10, 1896. On April 26, 1898, while at Fort Spokane in Washington, he was made a first lieutenant in the 7th Infantry on April 26, 1898. He remained at Spokane until June 1, 1898. Preston was them with the regiment in Tampa, Florida, until June 4, 1898, when he fought in the campaign against Santiago, and the Spanish–American War to August 1898. During that time he fought in the Battle of San Juan Hill on July 1–3, and in the Siege of Santiago until July 17, 1898. For his service in the war, he received the Silver Star "for gallantry in action against Spanish forces at Santiago, Cuba, July 1, 1898."