| Francis Butler Loomis | |
| Order: | 25th |
| United States Assistant Secretary of State | |
| Term Start: | January 7, 1903 |
| Term End: | October 10, 1905 |
| President: | Theodore Roosevelt |
| Predecessor: | David Jayne Hill |
| Successor: | Robert Bacon |
| Birth Date: | July 27, 1861 |
| Birth Place: | Marietta, Ohio, U.S. |
| Death Date: | August 4, 1948 (aged 87) |
| Death Place: | San Francisco, California, U.S. |
| Party: | Republican |
| Alma Mater: | Marietta College |
| Profession: | Journalist, Editor, Politician |
Francis Butler Loomis (July 27, 1861 – August 4, 1948) served as the United States Ambassador to Venezuela from 1897 to 1901 and the United States Ambassador to Portugal from 1901 to 1902. He was the United States Assistant Secretary of State from 1903 to 1905 when he was appointed as the acting United States Secretary of State. His son was Major general Francis B. Loomis Jr.
He was born on July 27, 1861.
He began his career as a newspaperman in his hometown of Marietta, Ohio, editing the Marietta Leader while a student at Marietta College. A year following his graduation in 1883, Loomis became a reporter for the New York Tribune and later assumed a campaign press relations position. He returned to Ohio to serve as state librarian for two years (from 1885 to 1887).
It was during the administration of President Benjamin Harrison that Loomis first entered government service as consul at Saint-Étienne, and at Grenoble, France, until 1893. For the next three years from 1893 to 1896, Loomis returned briefly to journalism as editor of the Cincinnati Daily Tribune. President William McKinley appointed him Ambassador to Venezuela in 1897 and to Portugal in 1901.
A year later, he was recalled to Washington, DC, and was appointed Assistant Secretary of State. On the death of Secretary John Hay, he served as acting Secretary of State briefly in 1905. During his State Department tenure, he became associated with the reorganization of the American Red Cross, serving as a charter member. His commissions included final negotiations which resulted in the acquisition of the Panama Canal Zone, service as special ambassador to France to receive the body of John Paul Jones and Special Envoy Extraordinary to Japan, arranging the visit of the U.S. fleet to that country in 1908. Shortly before World War I Loomis returned to private business as foreign trade adviser to the Standard Oil Company serving until retirement.
He died on August 4, 1948, in the San Francisco Bay area in California.