Born in Mönchengladbach and the son of a businessman, Theodor Hespers grew up in a middle-class Catholic family and completed commercial training. He joined the Catholic youth association Quickborn at the age of fifteen. In 1925, he became a member of the Christian Social Youth movement and later the Christian Social Reich Party. He toured the Soviet Union for eight weeks with a youth delegation in 1927. In the Westmark scouting group run by Hans Ebeling as part of the Young Nationalist League, he worked closely with the KPD to fight rising National Socialism in 1932.
Hespers had to emigrate to the Netherlands as early as April 1933. His wife joined him shortly later with their young son. In exile, Theodor Hespers continued his steadfast fight against National Socialism. He helped transport communist and Catholic publications to Germany and maintained contacts to members of the banned bündisch organizations.
He came back into contact with Hans Ebeling in exile in early 1936. Ebeling worked to unite bündisch and Catholic youth associations outside Germany, with Hespers' support. They founded the Working Group Bündische Jugend and published the youth journal Kameradschaft - Schriften junger Deutscher. In 1939, Hespers also began obtaining military intelligence for the British secret service. He lived in hiding in Belgium up until his arrest in February 1942.
The "People's Court" sentenced Theodor Hespers to death on July 22, 1943. He was murdered in Plötzensee prison on September 9, 1943, during the mass executions known as the bloody nights.