From 1914 Pilar was a member of the Russian Social Democratic Labour Party and was an active participant in the revolutionary movement.
[1] After the success of the February Revolution, from March 1917, Pilar was secretary of the Danilov Council of Peasants' Deputies.
From April 1918 he was one of the leaders of the party underground in Vilna and was elected chairman of the Military Revolutionary Committee of Lithuania.
From January 1919 Pilar was a member of the Presidium and secretary of the Central Executive Committee of the Lithuanian-Belarusian Socialist Soviet Republic.
When the Poles captured the headquarters of the workers' representatives on the street, he tried to shoot himself in Vilna, but survived (the bullet hit the lung).
In July 1922-December 1925, Deputy Head of the Counterintelligence Department (KRO) of the Secret Operational Directorate (SOU) of the GPU and OGPU of Artur Artuzov.
[1] On 2 September 1937, by the Decree of the Commission consisting of the People's Commissariat of Internal Affairs, the Procurator General of the Soviet Union and the Chairman of the All-Union Committee of the USSR Armed Forces, he was sentenced to capital punishment "in a special order" and was shot on the same day.
In July 1957, by the decision of the Supreme Court of the Soviet Union, the verdict was overturned and Pilar was rehabilitated.