A painter and print-maker. He studied painting at the School of Fine Arts in Athens, and print-making from 1900 to 1914 under professor N. Ferbos. He was self- taught in woodcut techniques.
He continued his studies after 1919 in England, France and Italy. From 1905-10 to 1922 he worked as a newspaper and magazine illustrator, signing his woodcuts and cartoons with the pseudonym Th. Angel or Th. Devil (1905 - 1910).
He became involved with advertising at GEO, one of the first advertising companies to operate in Greece, where he was appointed director in 1919. Theodoropoulos used a variety of engraving techniques, usually preferring the woodcut. His compositions of the woods of Attica are impressive, as are his still life compositions, skilfully executed in a Cubist mode.
Theodoropoulos worked in a more abstractive way in the 1960s, highlighting the merits of aquatint in the group of landscapes from the Cyclades (Santorini). Here he was interested more in the tonal gradations which are produced and less in the detailed description of the buildings, as was more his custom in the 1940s.