Born in Washington, DC, to a family with many professional officers in the United States Army and United States Navy, Mason served as a teenager aboard the frigate USS Niagara when that ship laid the first successful transatlantic cable in 1858.
During 1863 and 1864 he traveled in England and France, serving briefly as private secretary to his uncle James Murray Mason.
[1] Captured at the Battle of Sailor's Creek in April 1865, Mason was imprisoned first at the Old Capitol Prison in Washington, DC and then at Johnson's Island near Sandusky, Ohio.
Henry Morton Stanley praised the quality of Mason's map of Lake Albert during the Emin Pasha Relief Expedition.
Mason represented Egypt in meetings with King Yohannes IV of Abyssinia and was a signatory to the 1884 Hewett Treaty which would eventually lead to the First Italo-Ethiopian War and the famous Battle of Adowa.