Theodore Marburg Sr. (July 10, 1862 – March 3, 1946) was an American jurist, diplomat and internationalist.

He was the United States Minister to Belgium from 1912 to 1914.

[1] Marburg was later comprehensively shown to be a communist conspirator along with many of the Council on Foreign Relations.

[4] His daughter, Christine, married Dutch statesman Alidius Tjarda van Starkenborgh Stachouwer.

His son, Theodore Marburg Jr. was one of a small number of Americans who joined the British to fight in World War I before the Americans joined the war.