In November 1918, Angarietis returned to Lithuania and helped organizing the Communist Party of Lithuania (CPL) and Communist Party (Bolsheviks) of Lithuania and Belorussia. He became People's Commissar of Internal Affairs of the short-lived Lithuanian Soviet Socialist Republic (1918–1919) and Lithuanian–Belorussian Soviet Socialist Republic (Litbel). However, when Soviet Russia lost the Polish–Soviet and Lithuanian–Soviet Wars, these communist states collapsed and CPL was outlawed in Lithuania.