Leonas returned to Lithuania in 1919 and was mobilized on 1 July 1919 into the Lithuanian Army and assigned to the 8th Infantry Regiment. He saw action in the Lithuanian Wars of Independence against Soviet Russia (July 1919 – January 1920) and Poland (August–November 1920).[1] In February 1920, he helped to subdue a revolt by Lithuanian soldiers in Kaunas and was promoted to captain. He completed Higher Officers' Courses in October 1923 and was promoted to major. He retired from the military after graduating from the Law Faculty of University of Lithuania in 1925. He worked as a judge in Biržai, Telšiai, Šiauliai. After a judicial reform in 1933, he became a judge of the appellate court.[3]
On 16 June 1934, after the failed coup d'état by the Voldemarininkai, he returned to military duty and became the presiding judge of the Military Tribunal.[4] He presided over the high-profile trial of Neumann and Sass. The case involved 122 defendants – Nazi sympathizers that were accused of various anti-Lithuanian activities in the Klaipėda Region.[5] In March 1938, after the Polish ultimatum to Lithuania, he became Minister of Internal Affairs in the new cabinet assembled by Prime Minister Vladas Mironas.[1] In this capacity, Leonas issued many laws and directives, many of them on sale of pharmaceuticals, health clinics, and other health care issues. He also implemented the law establishing a council (Lithuanian: Visuomeninio darbo valdyba) to monitor and control various societies and organizations giving even more power to the authoritarian regime of Antanas Smetona to control political opponents.[3] The government was forced to resign after the German ultimatum to Lithuania in March 1939. He again retired from the military on 31 March 1939. In May 1940, Leonas was appointed as a judge of the Lithuanian Tribunal.[1]
123456Bitautas, Algis; Tamošaitis, Mindaugas (2016). "Leonas Silvestras". In Tamošaitis, Mindaugas; Bitautas, Algis; Svarauskas, Artūras (eds.). Lietuvos Respublikos 1918–1940 m. vyriausybių ministrų biografinis žodynas (in Lithuanian). Vilnius: Mokslo ir enciklopedijų leidybos centras. pp.247–249. ISBN978-5-420-01778-4.