In 1918, when socialist militants Gheorghe Cristescu, Alecu Constantinescu, and Ecaterina Arbore were arrested by the German authorities occupying southern Romania, Leon was one of the organisers of a public demonstration demanding their release.
In 1921 he went to Iași to support the local workers' movement, but soon returned to Bucharest, narrowly escaping arrest during the crackdown on the Socialist Conference taking place in the former city.
Pressure was put on his family to reveal his location, his home was repeatedly searched, his brother interrogated, while his sister was forced to sign a declaration condemning Leon's activities to be allowed to finish her studies at the Bucharest Conservatory.
For a short time in 1928 he was a member in Political Bureau of the Central Committee of the Communist Party of Romania, along with fellow exiles Fabian and Elek Köblös.
Leon Lichtblau was posthumously rehabilitated by a decision of the Soviet Supreme Court on October 3, 1956, as well as by a commission of the Romanian Communist Party in 1968.