Breckinridge attended the University of Tennessee in 1897 and 1898. He was appointed as a second lieutenant in the Marine Corps in 1899 to fight in the Spanish–American War, seeing service at Cavite in the Philippines. He was promoted to captain on July 23, 1901, serving as the commander of Marine detachments at sea through that decade. He served ashore in Panama and Nicaragua from late 1909 to early 1911, months later, temporary expeditionary duty in Cuba. In April 1914, he participated in the United States occupation of Veracruz while in command of the Marine attachment from the . He received a commendation for his conduct in battle.