He was the son of the notary Nikolaos Thomopoulos, and was born at 74 Ermou Street in Patras.

After service in the army, he returned to his native city to practice law.

In 1911, he was appointed to a post at the National Library of Greece following a competition, where he worked until his retirement in 1933.

In 1913, following the Balkan Wars, he was sent by the Ministry of Education to Macedonia to register the library collections in cities and monasteries in the areas of Florina, Korçë, Monastir and Kozani.

In 1888, at the age of 29, Thomopoulos published his first work, the first volume of his History of the City of Patras.