The Lithuanian Soviet Socialist Republic (LSSR) was a short-lived Soviet republic declared on December 16, 1918 by a provisional revolutionary government led by Vincas Mickevičius-Kapsukas.

It ceased to exist on February 27, 1919 when it was merged with the Socialist Soviet Republic of Byelorussia to form the Lithuanian–Belorussian Soviet Socialist Republic ("Litbel").

While efforts were made to represent the LSSR as a product of a socialist revolution supported by local residents, it was largely a Moscow-orchestrated entity created to justify the Lithuanian–Soviet War. The goal of the Soviet offensive was to follow retreating German troops and create Soviet republics in the regions they had vacated.

As a Soviet historian, adhering to official propaganda, put it: "The fact that the Government of Soviet Russia recognized a young Soviet Lithuanian Republic unmasked the lie of the USA and British imperialists that Soviet Russia allegedly sought rapacious aims with regard to the Baltic countries."

Lithuanians generally did not support Soviet causes and rallied for their own national state, declared independent on February 16, 1918, by the Council of Lithuania.

Between December 16, 1918 and January 7, 1920, the government resided in Daugavpils