Born into a Jewish family in Soroca, Bessarabia, Russian Empire (now in Moldova),[1] he joined the Romanian Communist Party (PCR) in the early 1930s.

[1] In 1956, Tismăneanu, alongside Dean Iorgu Iordan and the academics Mihai Novicov, Alexandru Graur, Ion Coteanu, and Radu Florian, took part in a university inquiry into the anti-communist statements of Paul Goma, a university student who later became a noted dissident and writer; led by Iordan and supervised by the Securitate, the investigation culminated in Goma's expulsion from the faculty and subsequent arrest (Tismăneanu and Florian voted in favor of the former, but against the latter).

[1] He was married to Hermina Marcusohn, herself a Spanish Civil War veteran who had trained as a physician, held a professorship at Bucharest's Medical School, and briefly worked as a party activist.

In an extended polemic with Vladimir Tismăneanu, Goma has indicated his mistrust in the latter's ability to exercise impartial judgment, allegedly calling him "a Bolshevik offspring".

[9] The Final Report of the Presidential Commission lists Leonte Tismăneanu among the group of prominent party activists responsible with indoctrination.